<PAGE>   1
      As filed with the Securities and Exchange Commission on June 12, 2001


                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                 --------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                               ------------------

                                  PLEXUS CORP.
             (Exact name of registrant as specified in its charter)

                 WISCONSIN                                    39-134447
      (State or other jurisdiction of                     (I.R.S. Employer
       incorporation or organization)                    Identification No.)

           55 JEWELERS PARK DRIVE
             NEENAH, WISCONSIN                                  54957
  (Address of Principal Executive Offices)                   (Zip Code)

                               ------------------

                      QTRON, INC. 1994 STOCK INCENTIVE PLAN
                            (Full title of the plan)
                               -------------------

                JOSEPH D. KAUFMAN                             Copy to:
  Vice President, Secretary and General Counsel          KENNETH V. HALLETT
                   PLEXUS CORP.                          Quarles & Brady LLP
              55 Jewelers Park Drive                  411 East Wisconsin Avenue
                   P.O. Box 156                      Milwaukee, Wisconsin 53202
           Neenah, Wisconsin 54957-0156

                     (Name and address of agent for service)

                                 (920) 722-3451
          (Telephone number, including area code, of agent for service)
                               -------------------


<PAGE>   2



                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
--------------------------------------------------------------------------------------------------------------------
  TITLE OF SECURITIES TO BE        AMOUNT TO BE           PROPOSED            PROPOSED              AMOUNT OF
         REGISTERED               REGISTERED (1)          MAXIMUM              MAXIMUM           REGISTRATION FEE
                                                       OFFERING PRICE         AGGREGATE
                                                        PER SHARE(2)      OFFERING PRICE(2)
--------------------------------------------------------------------------------------------------------------------
<S>                               <C>                  <C>               <C>                     <C>
Common Stock, par value $.01       5,596 shares          $2.17 (2)             $12,144                $3.04
          per share
--------------------------------------------------------------------------------------------------------------------
  Preferred Stock Purchase              (3)                 (3)                  (3)                   (3)
           Rights
--------------------------------------------------------------------------------------------------------------------
</TABLE>

(1)      The Plan provides for the possible adjustment of the number, price and
         kind of shares covered by options granted or to be granted in the event
         of certain capital or other changes affecting the Registrant's Common
         Stock. This Registration Statement therefore covers, in addition to the
         above-stated 5,596 shares, an indeterminate number of shares that may
         become subject to the Plan by means of any such adjustment.

(2)      Pursuant to Rule 457(h), estimated solely for the purpose of computing
         the registration fee, based upon $2.17 per share, which is the purchase
         price under outstanding options. The options were assumed by Plexus
         Corp. in its May 23, 2001 acquisition of Qtron, Inc. Plexus will not
         grant additional options under the Plan.

(3)      One right is issued in tandem with each share of Plexus common stock.
         The value attributable to the Preferred Stock Purchase Rights is
         reflected in the market price of the Common Stock to which the Rights
         are attached. Includes registration of shares of the Registrant's
         Preferred Stock and Common Stock underlying such rights.



                                      -2-
<PAGE>   3


                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

         Information specified in Part I of Form S-8 (Items 1 and 2) will be
sent or given to plan participants as specified by Rule 428(b)(1) under the
Securities Act of 1933.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by Plexus Corp. (the "Registrant")
(Commission File No. 000-44824) with the Securities and Exchange Commission
pursuant to Section 13 of the Securities Exchange Act of 1934, as amended are
incorporated herein by reference:

         (a)      The Registrant's Annual Report on Form 10-K for the fiscal
                  year ended September 30, 2000;

         (b)      The Registrant's Quarterly Reports on Form 10-Q for the
                  quarterly periods ended December 31, 2000 and March 31, 2001;

         (c)      The Registrant's Current Report on Form 8-K dated October 13,
                  2000;

         (d)      The financial statements of certain former operations of
                  Elamex, S.A. de C.V. included in the Registrant's Current
                  Report on Form 8-K dated May 23, 2000, as amended;

         (e)      The description of the Common Stock in the Registration
                  Statement on Form 8-A dated July 18, 1986, as amended; and

         (f)      The description of the Preferred Stock Purchase Rights in the
                  Registration Statement on Form 8-A, dated August 17, 1998, as
                  amended.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the 1934 Act, prior to the filing of a
post-effective amendment which indicates that all securities offered hereby have
been sold or which deregisters all securities then remaining unsold, shall be
deemed to be incorporated by reference herein and to be a part hereof from the
date of the filing of such documents.

         Any statement contained in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified or superseded
for purposes hereof to the extent that a statement contained herein or in any
other subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part hereof.




                                      -3-

<PAGE>   4


ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.  See Item 3(d) above.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         The legality of the shares of Common Stock registered hereunder are
being passed on for the Registrant by Quarles & Brady LLP, the Registrant's
legal counsel.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         The Registrant is incorporated under the Wisconsin Business Corporation
Law ("WBCL"). Under Section 180.0851(1) of the WBCL, the Registrant is required
to indemnify a director or officer, to the extent such person is successful on
the merits or otherwise in the defense of a proceeding, for all reasonable
expenses incurred in the proceeding if such person was a party because he or she
was a director or officer of the Registrant. In all other cases, the Registrant
is required by Section 180.0851(2) of the WBCL to indemnify a director or
officer against liability incurred in a proceeding to which such person was a
party because he or she was an officer or director of the Registrant, unless it
is determined that he or she breached or failed to perform a duty owed to the
Registrant and the breach or failure to perform constitutes: (i) a willful
failure to deal fairly with the Registrant or its shareholders in connection
with a matter in which the director or officer has a material conflict of
interest; (ii) a violation of criminal law, unless the director or officer had
reasonable cause to believe his or her conduct was lawful or no reasonable cause
to believe his or her conduct was unlawful; (iii) a transaction from which the
director or officer derived an improper personal profit; or (iv) willful
misconduct. Section 180.0858(1) of the WBCL provides that, subject to certain
limitations, the mandatory indemnification provisions do not preclude any
additional right to indemnification or allowance of expenses that a director or
officer may have under the Registrant's articles of incorporation, bylaws, a
written agreement or a resolution of the Board of Directors or shareholders.

         Section 180.0859 of the WBCL provides that it is the public policy of
the State of Wisconsin to require or permit indemnification, allowance of
expenses and insurance to the extent required or permitted under Sections
180.0850 to 180.0858 of the WBCL for any liability incurred in connection with a
proceeding involving a federal or state statute, rule or regulation regulating
the offer, sale or purchase of securities.

         Section 180.0828 of the WBCL provides that, with certain exceptions, a
director is not liable to a corporation, its shareholders, or any person
asserting rights on behalf of the corporation or its shareholders, for damages,
settlements, fees, fines, penalties or other monetary liabilities arising from a
breach of, or failure to perform, any duty resulting solely from his or her
status as a director, unless the person asserting liability proves that the
breach or failure to perform constitutes any of the four exceptions to mandatory
indemnification under Section 180.0851(2) referred to above.

         Under Section 180.0833 of the WBCL, directors of the Registrant against
whom claims are asserted with respect to the declaration of an improper dividend
or other distribution to shareholders to which they assented are entitled to
contribution from other directors who


                                      -4-
<PAGE>   5

assented to such distribution and from shareholders who knowingly accepted the
improper distribution, as provided therein.

         Article VIII of the Registrant's Bylaws contains provisions that
generally parallel the indemnification provisions of the WBCL and cover certain
procedural matters not dealt with in the WBCL. Directors and officers of the
Registrant are also covered by directors' and officers' liability insurance
under which they are insured (subject to certain exceptions and limitations
specified in the policy) against expenses and liabilities arising out of
proceedings to which they are parties by reason of being or having been
directors or officers.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

         See Exhibit Index following the signatures page in this Registration
Statement, which Exhibit Index is incorporated herein by reference.

ITEM 9.  UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act of
                                    1933;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the Registration Statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the Registration
                                    Statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not exceed
                                    that which was registered) and any deviation
                                    from the low or high end of the estimated
                                    maximum offering range may be reflected in
                                    the form of prospectus filed with the
                                    Commission pursuant to Rule 424(b) if, in
                                    the aggregate, the changes in volume and
                                    price represent no more than a 20% change in
                                    the maximum aggregate offering price set
                                    forth in the "Calculation of Registration
                                    Fee" table in the effective Registration
                                    Statement;

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the Registration
                                    Statement or any material change to such
                                    information in the Registration Statement;


                                      -5-
<PAGE>   6

                  Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) of
this section do not apply if the Registration Statement is on Form S-3 or Form
S-8, and the information required to be included in a post-effective amendment
by those paragraphs is contained in periodic reports filed by the Registrant
with the Commission pursuant to Section 13 or Section 15(d) of the Securities
Exchange Act of 1934 that are incorporated by reference in the Registration
Statement.

                  (2) That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)      The undersigned Registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  of 1933, each filing of the Registrant's annual report
                  pursuant to Section 13(a) or Section 15(d) of the Securities
                  Exchange Act of 1934 that is incorporated by reference in the
                  Registration Statement shall be deemed to be a new
                  registration statement relating to the securities offered
                  therein, and the offering of such securities at that time
                  shall be deemed to be the initial bona fide offering thereof.

         (h)      Reference is made to the indemnification provisions described
                  in Item 6 of this Registration Statement.

                  Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.




                                      -6-
<PAGE>   7


                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Neenah, State of Wisconsin, on June 11, 2001.

                                        PLEXUS CORP.
                                        (Registrant)


                                        By:  /s/ JOHN L. NUSSBAUM
                                            ---------------------
                                        John L. Nussbaum
                                        President and Chief Executive Officer

                               ------------------

                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
    appears below constitutes and appoints John L. Nussbaum, Thomas B. Sabol and
    Joseph D. Kaufman, and each of them, his true and lawful attorneys-in-fact
    and agents, with full power of substitution and resubstitution, for him and
    in his name, place and stead, in any and all capacities, to sign any and all
    amendments (including post-effective amendments) to this Registration
    Statement, and to file the same, with all exhibits thereto, and other
    documents in connection therewith, with the Securities and Exchange
    Commission, and any other regulatory authority, granting unto said
    attorneys-in-fact and agents, and each of them, full power and authority to
    do and perform each and every act and thing requisite and necessary to be
    done in and about the premises, as fully to all intents and purposes as he
    might or could do in person, hereby ratifying and confirming all that said
    attorneys-in-fact and agents or any of them, or their substitutes, may
    lawfully do or cause to be done by virtue hereof.

                              --------------------

         Pursuant to the requirements of the Securities Act of 1933, this
    Registration Statement has been signed by the following persons in the
    capacities and on the date indicated.*

<TABLE>
<S>                                                              <C>
                       /s/ JOHN L. NUSSBAUM                                /s/ HAROLD R. MILLER
      ------------------------------------------------------     --------------------------------------------------
      John L. Nussbaum,  President, Chief Executive Officer      Harold R. Miller, Director
      and Director (Principal Executive Officer)

                        /s/ THOMAS B. SABOL                                /s/ THOMAS J. PROSSER
      ------------------------------------------------------     ---------------------------------------------------
      Thomas  B.  Sabol,  Executive  Vice  President  and Chief  Thomas J. Prosser, Director
      Financial Officer (Principal Financial Officer)

                        /s/ LISA M. KELLEY                                 /s/ AGUSTIN A. RAMIREZ
      ------------------------------------------------------     ---------------------------------------------------
      Lisa  M.  Kelley,   Treasurer  and  Principal  Accounting  Agustin A. Ramirez, Director
      Officer

                        /s/ DAVID J. DRURY                                 /s/ PETER STRANDWITZ
      ------------------------------------------------------     ---------------------------------------------------
      David J. Drury, Director                                   Peter Strandwitz,  Chairman, Chief Executive Office
                                                                 and Director (Principal Executive Officer)

                         s/ DEAN A. FOATE                                  /s/ JAN K. VER HAGEN
      ------------------------------------------------------     --------------------------------------------------
      Dean A. Foate, Chief Operating Officer and Director        Jan K. Ver Hagen, Director
</TABLE>

            *Each of these signatures is affixed as of June 11, 2001.



                                      -7-
<PAGE>   8


                                  PLEXUS CORP.
                               (THE "REGISTRANT")
                          (COMMISSION FILE NO. 0-14553)

                                  EXHIBIT INDEX
                                       TO
                         FORM S-8 REGISTRATION STATEMENT

<TABLE>
<CAPTION>
EXHIBIT                 DESCRIPTION                              INCORPORATED HEREIN BY                      FILED HEREWITH
NUMBER                                                                 REFERENCE TO
<S>                <C>                                     <C>                                        <C>
4.1                Restated Articles of                    Exhibit 3(i) to Plexus' Quarterly
                   Incorporation of Plexus Corp.,          Report on Form 10-Q for the quarter
                   as amended through August 13,           ended March 31, 2001.
                   1998

4.2                Bylaws of Plexus Corp., as              Exhibit 3(ii) to Plexus' Quarterly
                   amended through November 14, 1996       Report on Form 10-Q for the quarter
                                                           ended December 31, 2000.

4.3                Shareholder Rights Plan dated as        Exhibit 4.1 to the Registrant's
                   of August 13, 1998 between the          Current Report on Form 8-K dated
                   Registrant and Firstar Trust Co.        August 13, 1998.

5                  Opinion of Quarles & Brady LLP                                                                    X

23.1               Consent of PricewaterhouseCoopers                                                                 X
                   LLP

23.2               Consent of Counsel                                                                 Contained in Opinion filed as
                                                                                                      Exhibit 5

23.3               Consent of Ernst & Young LLP                                                                      X

23.4               Consent of Deloitte & Touche LLP                                                                  X

24                 Powers of Attorney                                                                 Signature Page to this
                                                                                                      Registration Statement

99                 Qtron, Inc. 1994 Stock Incentive                                                                  X
                   Plan, as amended
</TABLE>



                                      -8-
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{"company-data": {"conformed-name": "PLEXUS CORP", "cik": "0000785786", "assigned-sic": "3672", "irs-number": "391344447", "state-of-incorporation": "WI", "fiscal-year-end": "0930"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-62774", "film-number": "1658929"}, "business-address": {"street1": "55 JEWELERS PARK DR", "city": "NEENAH", "state": "WI", "zip": "54957-0156", "phone": "9207223451"}, "mail-address": {"street1": "PLEXUS CORP", "street2": "55 JEWELERS PARK DR", "city": "NEENAH", "state": "WI", "zip": "54957-0156"}}
1
      As filed with the Securities and Exchange Commission on June 12, 2001

                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
                                 --------------
                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933
                               ------------------

                                  PLEXUS CORP.
             (Exact name of registrant as specified in its charter)

                 WISCONSIN                                    39-134447
      (State or other jurisdiction of                     (I.R.S. Employer
       incorporation or organization)                    Identification No.)

           55 JEWELERS PARK DRIVE
             NEENAH, WISCONSIN                                  54957
  (Address of Principal Executive Offices)                   (Zip Code)

                               ------------------

                      QTRON, INC. 1994 STOCK INCENTIVE PLAN
                            (Full title of the plan)
                               -------------------

                JOSEPH D. KAUFMAN                             Copy to:
  Vice President, Secretary and General Counsel          KENNETH V. HALLETT
                   PLEXUS CORP.                          Quarles & Brady LLP
              55 Jewelers Park Drive                  411 East Wisconsin Avenue
                   P.O. Box 156                      Milwaukee, Wisconsin 53202
           Neenah, Wisconsin 54957-0156

                     (Name and address of agent for service)

                                 (920) 722-3451
          (Telephone number, including area code, of agent for service)
                               -------------------
2

                         CALCULATION OF REGISTRATION FEE
--------------------------------------------------------------------------------------------------------------------
  TITLE OF SECURITIES TO BE        AMOUNT TO BE           PROPOSED            PROPOSED              AMOUNT OF
         REGISTERED               REGISTERED (1)          MAXIMUM              MAXIMUM           REGISTRATION FEE
                                                       OFFERING PRICE         AGGREGATE
                                                        PER SHARE(2)      OFFERING PRICE(2)
--------------------------------------------------------------------------------------------------------------------
Common Stock, par value $.01       5,596 shares          $2.17 (2)             $12,144                $3.04
          per share
--------------------------------------------------------------------------------------------------------------------
  Preferred Stock Purchase              (3)                 (3)                  (3)                   (3)
           Rights
--------------------------------------------------------------------------------------------------------------------
(1)      The Plan provides for the possible adjustment of the number, price and
         kind of shares covered by options granted or to be granted in the event
         of certain capital or other changes affecting the Registrant's Common
         Stock. This Registration Statement therefore covers, in addition to the
         above-stated 5,596 shares, an indeterminate number of shares that may
         become subject to the Plan by means of any such adjustment.

(2)      Pursuant to Rule 457(h), estimated solely for the purpose of computing
         the registration fee, based upon $2.17 per share, which is the purchase
         price under outstanding options. The options were assumed by Plexus
         Corp. in its May 23, 2001 acquisition of Qtron, Inc. Plexus will not
         grant additional options under the Plan.

(3)      One right is issued in tandem with each share of Plexus common stock.
         The value attributable to the Preferred Stock Purchase Rights is
         reflected in the market price of the Common Stock to which the Rights
         are attached. Includes registration of shares of the Registrant's
         Preferred Stock and Common Stock underlying such rights.

                                      -2-
3

                                     PART I

              INFORMATION REQUIRED IN THE SECTION 10(A) PROSPECTUS

         Information specified in Part I of Form S-8 (Items 1 and 2) will be
sent or given to plan participants as specified by Rule 428(b)(1) under the
Securities Act of 1933.

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

         The following documents filed by Plexus Corp. (the "Registrant")
(Commission File No. 000-44824) with the Securities and Exchange Commission
pursuant to Section 13 of the Securities Exchange Act of 1934, as amended are
incorporated herein by reference:

         (a)      The Registrant's Annual Report on Form 10-K for the fiscal
                  year ended September 30, 2000;

         (b)      The Registrant's Quarterly Reports on Form 10-Q for the
                  quarterly periods ended December 31, 2000 and March 31, 2001;

         (c)      The Registrant's Current Report on Form 8-K dated October 13,
                  2000;

         (d)      The financial statements of certain former operations of
                  Elamex, S.A. de C.V. included in the Registrant's Current
                  Report on Form 8-K dated May 23, 2000, as amended;

         (e)      The description of the Common Stock in the Registration
                  Statement on Form 8-A dated July 18, 1986, as amended; and

         (f)      The description of the Preferred Stock Purchase Rights in the
                  Registration Statement on Form 8-A, dated August 17, 1998, as
                  amended.

         All documents subsequently filed by the Registrant pursuant to Sections
13(a), 13(c), 14 and 15(d) of the 1934 Act, prior to the filing of a
post-effective amendment which indicates that all securities offered hereby have
been sold or which deregisters all securities then remaining unsold, shall be
deemed to be incorporated by reference herein and to be a part hereof from the
date of the filing of such documents.

         Any statement contained in a document incorporated or deemed to be
incorporated by reference herein shall be deemed to be modified or superseded
for purposes hereof to the extent that a statement contained herein or in any
other subsequently filed document which also is or is deemed to be incorporated
by reference herein modifies or supersedes such statement. Any statement so
modified or superseded shall not be deemed, except as so modified or superseded,
to constitute a part hereof.

                                      -3-
4

ITEM 4.  DESCRIPTION OF SECURITIES.

         Not applicable.  See Item 3(d) above.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         The legality of the shares of Common Stock registered hereunder are
being passed on for the Registrant by Quarles & Brady LLP, the Registrant's
legal counsel.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         The Registrant is incorporated under the Wisconsin Business Corporation
Law ("WBCL"). Under Section 180.0851(1) of the WBCL, the Registrant is required
to indemnify a director or officer, to the extent such person is successful on
the merits or otherwise in the defense of a proceeding, for all reasonable
expenses incurred in the proceeding if such person was a party because he or she
was a director or officer of the Registrant. In all other cases, the Registrant
is required by Section 180.0851(2) of the WBCL to indemnify a director or
officer against liability incurred in a proceeding to which such person was a
party because he or she was an officer or director of the Registrant, unless it
is determined that he or she breached or failed to perform a duty owed to the
Registrant and the breach or failure to perform constitutes: (i) a willful
failure to deal fairly with the Registrant or its shareholders in connection
with a matter in which the director or officer has a material conflict of
interest; (ii) a violation of criminal law, unless the director or officer had
reasonable cause to believe his or her conduct was lawful or no reasonable cause
to believe his or her conduct was unlawful; (iii) a transaction from which the
director or officer derived an improper personal profit; or (iv) willful
misconduct. Section 180.0858(1) of the WBCL provides that, subject to certain
limitations, the mandatory indemnification provisions do not preclude any
additional right to indemnification or allowance of expenses that a director or
officer may have under the Registrant's articles of incorporation, bylaws, a
written agreement or a resolution of the Board of Directors or shareholders.

         Section 180.0859 of the WBCL provides that it is the public policy of
the State of Wisconsin to require or permit indemnification, allowance of
expenses and insurance to the extent required or permitted under Sections
180.0850 to 180.0858 of the WBCL for any liability incurred in connection with a
proceeding involving a federal or state statute, rule or regulation regulating
the offer, sale or purchase of securities.

         Section 180.0828 of the WBCL provides that, with certain exceptions, a
director is not liable to a corporation, its shareholders, or any person
asserting rights on behalf of the corporation or its shareholders, for damages,
settlements, fees, fines, penalties or other monetary liabilities arising from a
breach of, or failure to perform, any duty resulting solely from his or her
status as a director, unless the person asserting liability proves that the
breach or failure to perform constitutes any of the four exceptions to mandatory
indemnification under Section 180.0851(2) referred to above.

         Under Section 180.0833 of the WBCL, directors of the Registrant against
whom claims are asserted with respect to the declaration of an improper dividend
or other distribution to shareholders to which they assented are entitled to
contribution from other directors who

                                      -4-
5

assented to such distribution and from shareholders who knowingly accepted the
improper distribution, as provided therein.

         Article VIII of the Registrant's Bylaws contains provisions that
generally parallel the indemnification provisions of the WBCL and cover certain
procedural matters not dealt with in the WBCL. Directors and officers of the
Registrant are also covered by directors' and officers' liability insurance
under which they are insured (subject to certain exceptions and limitations
specified in the policy) against expenses and liabilities arising out of
proceedings to which they are parties by reason of being or having been
directors or officers.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Not applicable.

ITEM 8.  EXHIBITS.

         See Exhibit Index following the signatures page in this Registration
Statement, which Exhibit Index is incorporated herein by reference.

ITEM 9.  UNDERTAKINGS.

         (a)      The undersigned Registrant hereby undertakes:

                  (1)      To file, during any period in which offers or sales
are being made, a post-effective amendment to this Registration Statement:

                           (i)      To include any prospectus required by
                                    Section 10(a)(3) of the Securities Act of
                                    1933;

                           (ii)     To reflect in the prospectus any facts or
                                    events arising after the effective date of
                                    the Registration Statement (or the most
                                    recent post-effective amendment thereof)
                                    which, individually or in the aggregate,
                                    represent a fundamental change in the
                                    information set forth in the Registration
                                    Statement. Notwithstanding the foregoing,
                                    any increase or decrease in volume of
                                    securities offered (if the total dollar
                                    value of securities offered would not exceed
                                    that which was registered) and any deviation
                                    from the low or high end of the estimated
                                    maximum offering range may be reflected in
                                    the form of prospectus filed with the
                                    Commission pursuant to Rule 424(b) if, in
                                    the aggregate, the changes in volume and
                                    price represent no more than a 20% change in
                                    the maximum aggregate offering price set
                                    forth in the "Calculation of Registration
                                    Fee" table in the effective Registration
                                    Statement;

                           (iii)    To include any material information with
                                    respect to the plan of distribution not
                                    previously disclosed in the Registration
                                    Statement or any material change to such
                                    information in the Registration Statement;

                                      -5-
6

                  Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) of
this section do not apply if the Registration Statement is on Form S-3 or Form
S-8, and the information required to be included in a post-effective amendment
by those paragraphs is contained in periodic reports filed by the Registrant
with the Commission pursuant to Section 13 or Section 15(d) of the Securities
Exchange Act of 1934 that are incorporated by reference in the Registration
Statement.

                  (2) That, for the purpose of determining any liability under
the Securities Act of 1933, each such post-effective amendment shall be deemed
to be a new registration statement relating to the securities offered therein,
and the offering of such securities at that time shall be deemed to be the
initial bona fide offering thereof.

                  (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)      The undersigned Registrant hereby undertakes that, for
                  purposes of determining any liability under the Securities Act
                  of 1933, each filing of the Registrant's annual report
                  pursuant to Section 13(a) or Section 15(d) of the Securities
                  Exchange Act of 1934 that is incorporated by reference in the
                  Registration Statement shall be deemed to be a new
                  registration statement relating to the securities offered
                  therein, and the offering of such securities at that time
                  shall be deemed to be the initial bona fide offering thereof.

         (h)      Reference is made to the indemnification provisions described
                  in Item 6 of this Registration Statement.

                  Insofar as indemnification for liabilities arising under the
Securities Act of 1933 may be permitted to directors, officers and controlling
persons of the Registrant pursuant to the foregoing provisions, or otherwise,
the Registrant has been advised that in the opinion of the Securities and
Exchange Commission such indemnification is against public policy as expressed
in the Act and is, therefore, unenforceable. In the event that a claim for
indemnification against such liabilities (other than the payment by the
Registrant of expenses incurred or paid by a director, officer or controlling
person of the Registrant in the successful defense of any action, suit or
proceeding) is asserted by such director, officer or controlling person in
connection with the securities being registered, the Registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit to a court of appropriate jurisdiction the question whether such
indemnification by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

                                      -6-
7

                                   SIGNATURES

         Pursuant to the requirements of the Securities Act of 1933, the
Registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Neenah, State of Wisconsin, on June 11, 2001.

                                        PLEXUS CORP.
                                        (Registrant)

                                        By:  /s/ JOHN L. NUSSBAUM
                                            ---------------------
                                        John L. Nussbaum
                                        President and Chief Executive Officer

                               ------------------

                                POWER OF ATTORNEY

         KNOW ALL MEN BY THESE PRESENTS, that each person whose signature
    appears below constitutes and appoints John L. Nussbaum, Thomas B. Sabol and
    Joseph D. Kaufman, and each of them, his true and lawful attorneys-in-fact
    and agents, with full power of substitution and resubstitution, for him and
    in his name, place and stead, in any and all capacities, to sign any and all
    amendments (including post-effective amendments) to this Registration
    Statement, and to file the same, with all exhibits thereto, and other
    documents in connection therewith, with the Securities and Exchange
    Commission, and any other regulatory authority, granting unto said
    attorneys-in-fact and agents, and each of them, full power and authority to
    do and perform each and every act and thing requisite and necessary to be
    done in and about the premises, as fully to all intents and purposes as he
    might or could do in person, hereby ratifying and confirming all that said
    attorneys-in-fact and agents or any of them, or their substitutes, may
    lawfully do or cause to be done by virtue hereof.

                              --------------------

         Pursuant to the requirements of the Securities Act of 1933, this
    Registration Statement has been signed by the following persons in the
    capacities and on the date indicated.*
/s/ JOHN L. NUSSBAUM                                /s/ HAROLD R. MILLER
      ------------------------------------------------------     --------------------------------------------------
      John L. Nussbaum,  President, Chief Executive Officer      Harold R. Miller, Director
      and Director (Principal Executive Officer)

                        /s/ THOMAS B. SABOL                                /s/ THOMAS J. PROSSER
      ------------------------------------------------------     ---------------------------------------------------
      Thomas  B.  Sabol,  Executive  Vice  President  and Chief  Thomas J. Prosser, Director
      Financial Officer (Principal Financial Officer)

                        /s/ LISA M. KELLEY                                 /s/ AGUSTIN A. RAMIREZ
      ------------------------------------------------------     ---------------------------------------------------
      Lisa  M.  Kelley,   Treasurer  and  Principal  Accounting  Agustin A. Ramirez, Director
      Officer

                        /s/ DAVID J. DRURY                                 /s/ PETER STRANDWITZ
      ------------------------------------------------------     ---------------------------------------------------
      David J. Drury, Director                                   Peter Strandwitz,  Chairman, Chief Executive Office
                                                                 and Director (Principal Executive Officer)

                         s/ DEAN A. FOATE                                  /s/ JAN K. VER HAGEN
      ------------------------------------------------------     --------------------------------------------------
      Dean A. Foate, Chief Operating Officer and Director        Jan K. Ver Hagen, Director
*Each of these signatures is affixed as of June 11, 2001.

                                      -7-
8

                                  PLEXUS CORP.
                               (THE "REGISTRANT")
                          (COMMISSION FILE NO. 0-14553)

                                  EXHIBIT INDEX
                                       TO
                         FORM S-8 REGISTRATION STATEMENT
EXHIBIT                 DESCRIPTION                              INCORPORATED HEREIN BY                      FILED HEREWITH
NUMBER                                                                 REFERENCE TO
4.1                Restated Articles of                    Exhibit 3(i) to Plexus' Quarterly
                   Incorporation of Plexus Corp.,          Report on Form 10-Q for the quarter
                   as amended through August 13,           ended March 31, 2001.
                   1998

4.2                Bylaws of Plexus Corp., as              Exhibit 3(ii) to Plexus' Quarterly
                   amended through November 14, 1996       Report on Form 10-Q for the quarter
                                                           ended December 31, 2000.

4.3                Shareholder Rights Plan dated as        Exhibit 4.1 to the Registrant's
                   of August 13, 1998 between the          Current Report on Form 8-K dated
                   Registrant and Firstar Trust Co.        August 13, 1998.

5                  Opinion of Quarles & Brady LLP                                                                    X

23.1               Consent of PricewaterhouseCoopers                                                                 X
                   LLP

23.2               Consent of Counsel                                                                 Contained in Opinion filed as
                                                                                                      Exhibit 5

23.3               Consent of Ernst & Young LLP                                                                      X

23.4               Consent of Deloitte & Touche LLP                                                                  X

24                 Powers of Attorney                                                                 Signature Page to this
                                                                                                      Registration Statement

99                 Qtron, Inc. 1994 Stock Incentive                                                                  X
                   Plan, as amended
-8-