<PAGE>   1
      As filed with the Securities and Exchange Commission on May 14, 2001
                                                      Registration No. 333-_____
================================================================================

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

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

                             KLA-TENCOR CORPORATION
             (Exact name of Registrant as specified in its charter)

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

        DELAWARE                                        04-2564110
------------------------                 ---------------------------------------
(State of Incorporation)                 (I.R.S. Employer Identification Number)

                                 160 RIO ROBLES
                               SAN JOSE, CA 95134
                    (Address of Principal Executive Offices)

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

                         2000 NONSTATUTORY STOCK OPTION
                                      PLAN
                            (Full title of the plan)

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

                                STUART J. NICHOLS
                       VICE PRESIDENT AND GENERAL COUNSEL
                             KLA-TENCOR CORPORATION
                                 160 RIO ROBLES
                               SAN JOSE, CA 95134
                     (Name and address of agent for service)
                                 (408) 875-4200
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:
                             Larry W. Sonsini, Esq.
                              Bret M. DiMarco, Esq.
                     WILSON SONSINI GOODRICH & ROSATI, P.C.
                               650 Page Mill Road
                            Palo Alto, CA 94304-1050
                                 (650) 493-9300

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

<TABLE>
<CAPTION>
                                                CALCULATION OF REGISTRATION FEE
=================================================================================================================================
                                                       AMOUNT        PROPOSED MAXIMUM     PROPOSED MAXIMUM
                TITLE OF SECURITIES TO                 TO BE           OFFERING PRICE    AGGREGATE OFFERING        AMOUNT OF
                    BE REGISTERED                   REGISTERED(1)       PER SHARE(2)            PRICE           REGISTRATION FEE
------------------------------------------------- ----------------- ------------------- --------------------- -------------------
<S>                                                  <C>                  <C>             <C>                     <C>
      Common Stock, $.001 par value (3)              5,600,000            $49.60          $277,760,000.00         $69,440.00
---------------------------------------------------------------------------------------------------------------------------------
</TABLE>

(1)  Pursuant to Rule 416(a) under the Securities Act of 1933, as amended (the
     "Securities Act"), this Registration Statement shall also cover any
     additional shares of the Registrant's Common Stock that become issuable
     under the 2000 Nonstatutory Plan described herein (the "Plan") by reason of
     any stock dividend, stock split, recapitalization or other similar
     transaction effected without the Registrant's receipt of consideration that
     results in an increase in the number of the Registrant's outstanding shares
     of Common Stock.
(2)  Estimated solely for the purpose of calculating the registration fee
     pursuant to Rule 457(c) in accordance with Rule 457(h) under the Securities
     Act, on the basis of $49.60 per share, the average of the high and low
     prices per share of the Common Stock on the NASDAQ National Market on May
     9, 2001.
(3)  Associated with the Common Stock are Common Stock Purchase Rights that will
     not be exercisable until the occurrence of certain prescribed events, none
     of which has occurred.

<PAGE>   2
                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

         KLA-Tencor Corporation (the "Company" or the "Registrant") hereby
incorporates the following documents by reference in this registration
statement:

         (a)  The Company's Annual Report on Form 10-K for the fiscal year ended
              June 30, 2000, filed on September 28, 2000;

         (b)  The Company's Quarterly Report on Form 10-Q for the quarterly
              period ended September 30, 2000, filed on November 14, 2000;

         (c)  The Company's Quarterly Report on Form 10-Q for the quarterly
              period ended December 31, 2000, filed on February 14, 2001;

         (d)  The Company's Current Report on Form 8-K, filed on December 20,
              2000;

         (e)  The Company's Current Report on Form 8-K, filed on March 21, 2001;

         (f)  All other reports filed by the Company pursuant to Section 13(a)
              or 15(d) of the Securities Exchange Act of 1934, as amended (the
              "Exchange Act") since the end of the fiscal year covered by the
              Annual Report on Form 10-K referred to in (a) above;

         (g)  Item 1 of the Company's Registration Statement on Form 8-A, filed
              on March 29, 1989;

         (h)  Item 1 of the Company's Amendment No. 2 to its Registration
              Statement on Form 8-A/A, filed on September 24, 1996; and

         (i)  All other descriptions of the Company's Common Stock contained in
              a registration statement filed under the Exchange Act, including
              any amendment or report filed for the purpose of updating such
              description.

         All documents filed by the Company pursuant to Sections 13(a), 13(c),
14 and 15(d) of the Exchange Act, on or after the date of this registration
statement and prior to the filing of a post-effective amendment which indicates
that all securities offered have been sold or which deregisters all securities
then remaining unsold, shall be deemed to be incorporated by reference in this
registration statement and to be part hereof from the date of filing of such
documents.

ITEM 4. DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.


                                      II-1
<PAGE>   3
ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145(a) of the Delaware General Corporation Law (the "DGCL")
provides in relevant part that "[a] corporation may indemnify any person who was
or is a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of the corporation) by
reason of the fact that he is or was a director, officer, employee or agent of
the corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful."
With respect to derivative actions, Section 145(b) of the DGCL provides in
relevant part that "[a] corporation may indemnify any person who was or is a
party or is threatened to be made a party to any threatened, pending or
completed action or suit by or in the right of the corporation to procure a
judgment in its favor... [by reason of his service in one of the capacities
specified in the preceding sentence] against expenses (including attorneys'
fees) actually and reasonably incurred by him in connection with the defense or
settlement of such action or suit if he acted in good faith and in a manner he
reasonably believed to be in or not opposed to the best interests of the
corporation and except that no indemnification shall be made in respect of any
claim, issue or matter as to which such person shall have been adjudged to be
liable to the corporation unless and only to the extent that the Court of
Chancery or the court in which such action or suit was brought shall determine
upon application that, despite the adjudication of liability but in view of all
the circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses which the Court of Chancery or such other court
shall deem proper."

         The Registrant's Amended and Restated Certificate of Incorporation
provides that to the fullest extent permitted by the DGCL, no director of the
Registrant shall be personally liable to the Registrant or its stockholders for
monetary damages for breach of fiduciary duty as a director. The Amended and
Restated Certificate of Incorporation also provides that no amendment or repeal
of such provision shall apply to or have any effect on the right to
indemnification permitted thereunder with respect to claims arising from acts or
omissions occurring in whole or in part before the effective date of such
amendment or repeal whether asserted before or after such amendment or repeal.

         The Registrant's Bylaws provide that the Registrant shall indemnify to
the fullest extent permitted by the DGCL each of its directors, officers,
employees and other agents against expenses actually and reasonably incurred in
connection with any proceeding arising by reason of the fact that such person is
or was an agent of the Registrant.

         The Registrant has entered into indemnification agreements with its
directors and executive officers and intends to enter into indemnification
agreements with any new directors and executive officers in the future.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

         Not Applicable

                                      II-2
<PAGE>   4

ITEM 8. EXHIBITS.

<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER                                        DESCRIPTION
     ----------                                 ---------------------
<S>                        <C>
         4.1*              Amended and Restated Certificate of Incorporation of the Company
         4.2**             Bylaws of the Company, as amended
         4.3***            2000 Nonstatutory Stock Option Plan
         5.1               Opinion of counsel as to legality of securities being registered
        23.1               Consent of independent accountants
        23.2               Consent of counsel (contained in Exhibit 5.1)
        24.1               Power of attorney
</TABLE>
-----------

*      Incorporated by reference to Exhibit 3.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).

**     Incorporated by reference to Exhibit 3.2 of the Company's Registration
       Statement on Form S-8, filed on December 4, 1998 (File No. 333-68415).

***    Incorporated by reference to Exhibit 10.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).


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, as amended (the "Securities Act");

                  (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;

                  (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;

Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Registrant pursuant to
Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act") that are incorporated by reference in the registration
statement.

              (2) That, for the purpose of determining any liability under the
Securities Act 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.

                                      II-3
<PAGE>   5

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) 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.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act 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 Securities Act and will be governed by the final
adjudication of such issue.

                                      II-4
<PAGE>   6



                                   SIGNATURES

THE REGISTRANT

         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 San Jose, State of California, on May 14, 2001.

KLA-TENCOR CORPORATION

/s/ Stuart J. Nichols
-----------------------------------------------------
Stuart J. Nichols, Vice President and General Counsel


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
dates indicated.

<TABLE>
<CAPTION>
                   Signature                                    Title                               Date
<S>                                                 <C>                                         <C>
          Principal Executive Officer:


           /s/ Kenneth L. Schroeder                 President and Chief Executive               May 14, 2001
           -------------------------                           Officer
              Kenneth L. Schroeder

Principal Financial and
   Accounting Officer:

           /s/ John Kispert                          Executive Vice President and               May 14, 2001
           -------------------------                   Chief Financial Officer
                 John Kispert
</TABLE>

                                      II-5

<PAGE>   7
<TABLE>
<CAPTION>
                   Signature                                    Title                               Date
<S>                                                 <C>                                         <C>
                   Directors:

           /s/ Kenneth Levy                       Chairman of the Board and Director            May 14, 2001
           -------------------------
                  Kenneth Levy

           /s/ Edward W. Barnholt                              Director                         May 14, 2001
           -------------------------
               Edward W. Barnholt

           /s/ Richard J. Elkus, Jr.                           Director                         May 14, 2001
           -------------------------
             Richard J. Elkus, Jr.

           /s/ Dean O. Morton                                  Director                         May 14, 2001
           -------------------------
                 Dean O. Morton

           /s/ Jon D. Tompkins                                 Director                         May 14, 2001
           -------------------------
                Jon D. Tompkins

           /s/ Lida Urbanek                                    Director                         May 14, 2001
           -------------------------
                  Lida Urbanek

           /s/ H. Raymond Bingham                              Director                         May 14, 2001
           -------------------------
               H. Raymond Bingham

           /s/ Kenneth L. Schroeder                            Director                         May 14, 2001
           -------------------------
              Kenneth L. Schroeder

           /s/ Robert T. Bond                                  Director                         May 14, 2001
           -------------------------
                 Robert T. Bond

       *By /s/ Stuart J. Nichols
           -------------------------
               Stuart J. Nichols
                Attorney-in-Fact
</TABLE>

A majority of the members of the Board of Directors.


                                      II-6
<PAGE>   8




                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>
       EXHIBIT
       NUMBER                                        DESCRIPTION
     ----------                                 ---------------------
<S>                        <C>
         4.1*              Amended and Restated Certificate of Incorporation of the Company
         4.2**             Bylaws of the Company, as amended
         4.3***            2000 Nonstatutory Stock Option Plan
         5.1               Opinion of counsel as to legality of securities being registered
        23.1               Consent of independent accountants
        23.2               Consent of counsel (contained in Exhibit 5.1)
        24.1               Power of attorney
</TABLE>
-----------

*      Incorporated by reference to Exhibit 3.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).

**     Incorporated by reference to Exhibit 3.2 of the Company's Registration
       Statement on Form S-8, filed on December 4, 1998 (File No. 333-68415).

***    Incorporated by reference to Exhibit 10.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).
[{"type": "S-8", "sequence": "1", "filename": "f72485ors-8.txt", "description": "S-8", "secsgml_size_bytes": 20959}]
{"company-data": {"conformed-name": "KLA TENCOR CORP", "cik": "0000319201", "assigned-sic": "3827", "irs-number": "042564110", "state-of-incorporation": "DE", "fiscal-year-end": "0630"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-60864", "film-number": "1633455"}, "business-address": {"street1": "160 RIO ROBLES", "city": "SAN JOSE", "state": "CA", "zip": "95134", "phone": "4084344200"}, "mail-address": {"street1": "160 RIO ROBLES", "city": "SAN JOSE", "state": "CA", "zip": "95161-9055"}, "former-company": {"former-conformed-name": "KLA INSTRUMENTS CORP", "date-changed": "19920703"}}
1
      As filed with the Securities and Exchange Commission on May 14, 2001
                                                      Registration No. 333-_____
================================================================================

                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549

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

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      UNDER
                           THE SECURITIES ACT OF 1933

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

                             KLA-TENCOR CORPORATION
             (Exact name of Registrant as specified in its charter)

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

        DELAWARE                                        04-2564110
------------------------                 ---------------------------------------
(State of Incorporation)                 (I.R.S. Employer Identification Number)

                                 160 RIO ROBLES
                               SAN JOSE, CA 95134
                    (Address of Principal Executive Offices)

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

                         2000 NONSTATUTORY STOCK OPTION
                                      PLAN
                            (Full title of the plan)

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

                                STUART J. NICHOLS
                       VICE PRESIDENT AND GENERAL COUNSEL
                             KLA-TENCOR CORPORATION
                                 160 RIO ROBLES
                               SAN JOSE, CA 95134
                     (Name and address of agent for service)
                                 (408) 875-4200
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:
                             Larry W. Sonsini, Esq.
                              Bret M. DiMarco, Esq.
                     WILSON SONSINI GOODRICH & ROSATI, P.C.
                               650 Page Mill Road
                            Palo Alto, CA 94304-1050
                                 (650) 493-9300

                              --------------------
CALCULATION OF REGISTRATION FEE
=================================================================================================================================
                                                       AMOUNT        PROPOSED MAXIMUM     PROPOSED MAXIMUM
                TITLE OF SECURITIES TO                 TO BE           OFFERING PRICE    AGGREGATE OFFERING        AMOUNT OF
                    BE REGISTERED                   REGISTERED(1)       PER SHARE(2)            PRICE           REGISTRATION FEE
------------------------------------------------- ----------------- ------------------- --------------------- -------------------
Common Stock, $.001 par value (3)              5,600,000            $49.60          $277,760,000.00         $69,440.00
---------------------------------------------------------------------------------------------------------------------------------
(1)  Pursuant to Rule 416(a) under the Securities Act of 1933, as amended (the
     "Securities Act"), this Registration Statement shall also cover any
     additional shares of the Registrant's Common Stock that become issuable
     under the 2000 Nonstatutory Plan described herein (the "Plan") by reason of
     any stock dividend, stock split, recapitalization or other similar
     transaction effected without the Registrant's receipt of consideration that
     results in an increase in the number of the Registrant's outstanding shares
     of Common Stock.
(2)  Estimated solely for the purpose of calculating the registration fee
     pursuant to Rule 457(c) in accordance with Rule 457(h) under the Securities
     Act, on the basis of $49.60 per share, the average of the high and low
     prices per share of the Common Stock on the NASDAQ National Market on May
     9, 2001.
(3)  Associated with the Common Stock are Common Stock Purchase Rights that will
     not be exercisable until the occurrence of certain prescribed events, none
     of which has occurred.
2
                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 3. INCORPORATION OF DOCUMENTS BY REFERENCE.

         KLA-Tencor Corporation (the "Company" or the "Registrant") hereby
incorporates the following documents by reference in this registration
statement:

         (a)  The Company's Annual Report on Form 10-K for the fiscal year ended
              June 30, 2000, filed on September 28, 2000;

         (b)  The Company's Quarterly Report on Form 10-Q for the quarterly
              period ended September 30, 2000, filed on November 14, 2000;

         (c)  The Company's Quarterly Report on Form 10-Q for the quarterly
              period ended December 31, 2000, filed on February 14, 2001;

         (d)  The Company's Current Report on Form 8-K, filed on December 20,
              2000;

         (e)  The Company's Current Report on Form 8-K, filed on March 21, 2001;

         (f)  All other reports filed by the Company pursuant to Section 13(a)
              or 15(d) of the Securities Exchange Act of 1934, as amended (the
              "Exchange Act") since the end of the fiscal year covered by the
              Annual Report on Form 10-K referred to in (a) above;

         (g)  Item 1 of the Company's Registration Statement on Form 8-A, filed
              on March 29, 1989;

         (h)  Item 1 of the Company's Amendment No. 2 to its Registration
              Statement on Form 8-A/A, filed on September 24, 1996; and

         (i)  All other descriptions of the Company's Common Stock contained in
              a registration statement filed under the Exchange Act, including
              any amendment or report filed for the purpose of updating such
              description.

         All documents filed by the Company pursuant to Sections 13(a), 13(c),
14 and 15(d) of the Exchange Act, on or after the date of this registration
statement and prior to the filing of a post-effective amendment which indicates
that all securities offered have been sold or which deregisters all securities
then remaining unsold, shall be deemed to be incorporated by reference in this
registration statement and to be part hereof from the date of filing of such
documents.

ITEM 4. DESCRIPTION OF SECURITIES.

         Not applicable.

ITEM 5. INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Not applicable.

                                      II-1
3
ITEM 6. INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         Section 145(a) of the Delaware General Corporation Law (the "DGCL")
provides in relevant part that "[a] corporation may indemnify any person who was
or is a party or is threatened to be made a party to any threatened, pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative (other than an action by or in the right of the corporation) by
reason of the fact that he is or was a director, officer, employee or agent of
the corporation, or is or was serving at the request of the corporation as a
director, officer, employee or agent of another corporation, partnership, joint
venture, trust or other enterprise, against expenses (including attorneys'
fees), judgments, fines and amounts paid in settlement actually and reasonably
incurred by him in connection with such action, suit or proceeding if he acted
in good faith and in a manner he reasonably believed to be in or not opposed to
the best interests of the corporation, and, with respect to any criminal action
or proceeding, had no reasonable cause to believe his conduct was unlawful."
With respect to derivative actions, Section 145(b) of the DGCL provides in
relevant part that "[a] corporation may indemnify any person who was or is a
party or is threatened to be made a party to any threatened, pending or
completed action or suit by or in the right of the corporation to procure a
judgment in its favor... [by reason of his service in one of the capacities
specified in the preceding sentence] against expenses (including attorneys'
fees) actually and reasonably incurred by him in connection with the defense or
settlement of such action or suit if he acted in good faith and in a manner he
reasonably believed to be in or not opposed to the best interests of the
corporation and except that no indemnification shall be made in respect of any
claim, issue or matter as to which such person shall have been adjudged to be
liable to the corporation unless and only to the extent that the Court of
Chancery or the court in which such action or suit was brought shall determine
upon application that, despite the adjudication of liability but in view of all
the circumstances of the case, such person is fairly and reasonably entitled to
indemnity for such expenses which the Court of Chancery or such other court
shall deem proper."

         The Registrant's Amended and Restated Certificate of Incorporation
provides that to the fullest extent permitted by the DGCL, no director of the
Registrant shall be personally liable to the Registrant or its stockholders for
monetary damages for breach of fiduciary duty as a director. The Amended and
Restated Certificate of Incorporation also provides that no amendment or repeal
of such provision shall apply to or have any effect on the right to
indemnification permitted thereunder with respect to claims arising from acts or
omissions occurring in whole or in part before the effective date of such
amendment or repeal whether asserted before or after such amendment or repeal.

         The Registrant's Bylaws provide that the Registrant shall indemnify to
the fullest extent permitted by the DGCL each of its directors, officers,
employees and other agents against expenses actually and reasonably incurred in
connection with any proceeding arising by reason of the fact that such person is
or was an agent of the Registrant.

         The Registrant has entered into indemnification agreements with its
directors and executive officers and intends to enter into indemnification
agreements with any new directors and executive officers in the future.

ITEM 7. EXEMPTION FROM REGISTRATION CLAIMED.

         Not Applicable

                                      II-2
4

ITEM 8. EXHIBITS.
EXHIBIT
       NUMBER                                        DESCRIPTION
     ----------                                 ---------------------
4.1*              Amended and Restated Certificate of Incorporation of the Company
         4.2**             Bylaws of the Company, as amended
         4.3***            2000 Nonstatutory Stock Option Plan
         5.1               Opinion of counsel as to legality of securities being registered
        23.1               Consent of independent accountants
        23.2               Consent of counsel (contained in Exhibit 5.1)
        24.1               Power of attorney
-----------

*      Incorporated by reference to Exhibit 3.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).

**     Incorporated by reference to Exhibit 3.2 of the Company's Registration
       Statement on Form S-8, filed on December 4, 1998 (File No. 333-68415).

***    Incorporated by reference to Exhibit 10.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).

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, as amended (the "Securities Act");

                  (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;

                  (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;

Provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) do not apply if the
information required to be included in a post-effective amendment by those
paragraphs is contained in periodic reports filed by the Registrant pursuant to
Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended
(the "Exchange Act") that are incorporated by reference in the registration
statement.

              (2) That, for the purpose of determining any liability under the
Securities Act 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.

                                      II-3
5

         (b) The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) 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.

         (c) Insofar as indemnification for liabilities arising under the
Securities Act 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 Securities Act and will be governed by the final
adjudication of such issue.

                                      II-4
6

                                   SIGNATURES

THE REGISTRANT

         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 San Jose, State of California, on May 14, 2001.

KLA-TENCOR CORPORATION

/s/ Stuart J. Nichols
-----------------------------------------------------
Stuart J. Nichols, Vice President and General Counsel

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
dates indicated.
Signature                                    Title                               Date
Principal Executive Officer:

           /s/ Kenneth L. Schroeder                 President and Chief Executive               May 14, 2001
           -------------------------                           Officer
              Kenneth L. Schroeder

Principal Financial and
   Accounting Officer:

           /s/ John Kispert                          Executive Vice President and               May 14, 2001
           -------------------------                   Chief Financial Officer
                 John Kispert
II-5
7
Signature                                    Title                               Date
Directors:

           /s/ Kenneth Levy                       Chairman of the Board and Director            May 14, 2001
           -------------------------
                  Kenneth Levy

           /s/ Edward W. Barnholt                              Director                         May 14, 2001
           -------------------------
               Edward W. Barnholt

           /s/ Richard J. Elkus, Jr.                           Director                         May 14, 2001
           -------------------------
             Richard J. Elkus, Jr.

           /s/ Dean O. Morton                                  Director                         May 14, 2001
           -------------------------
                 Dean O. Morton

           /s/ Jon D. Tompkins                                 Director                         May 14, 2001
           -------------------------
                Jon D. Tompkins

           /s/ Lida Urbanek                                    Director                         May 14, 2001
           -------------------------
                  Lida Urbanek

           /s/ H. Raymond Bingham                              Director                         May 14, 2001
           -------------------------
               H. Raymond Bingham

           /s/ Kenneth L. Schroeder                            Director                         May 14, 2001
           -------------------------
              Kenneth L. Schroeder

           /s/ Robert T. Bond                                  Director                         May 14, 2001
           -------------------------
                 Robert T. Bond

       *By /s/ Stuart J. Nichols
           -------------------------
               Stuart J. Nichols
                Attorney-in-Fact
A majority of the members of the Board of Directors.

                                      II-6
8

                                INDEX TO EXHIBITS
EXHIBIT
       NUMBER                                        DESCRIPTION
     ----------                                 ---------------------
4.1*              Amended and Restated Certificate of Incorporation of the Company
         4.2**             Bylaws of the Company, as amended
         4.3***            2000 Nonstatutory Stock Option Plan
         5.1               Opinion of counsel as to legality of securities being registered
        23.1               Consent of independent accountants
        23.2               Consent of counsel (contained in Exhibit 5.1)
        24.1               Power of attorney
-----------

*      Incorporated by reference to Exhibit 3.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).

**     Incorporated by reference to Exhibit 3.2 of the Company's Registration
       Statement on Form S-8, filed on December 4, 1998 (File No. 333-68415).

***    Incorporated by reference to Exhibit 10.1 of the Company's Quarterly
       Report on Form 10-Q for the quarterly period ended December 31, 2000,
       filed on February 14, 2001 (File No. 000-09992).