<PAGE>   1
     As filed with the Securities and Exchange Commission on August 13, 1999
                                                   Registration No. 333-
================================================================================

                       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 No.)

                                 160 Rio Robles
                           San Jose, California 95134
          (Address, including zip code, of principal executive offices)


                        1997 EMPLOYEE STOCK PURCHASE PLAN
                           (Full Titles of the Plans)

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

                                ROBERT J. BOEHLKE
                EXECUTIVE VICE PRESIDENT, CHIEF FINANCIAL OFFICER
                             KLA-TENCOR CORPORATION
                                 160 Rio Robles
                           San Jose, California 95134
                     (Name and address of agent for service)
                                 (408) 434-4200
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:
                             JUDITH M. O'BRIEN, ESQ.
                        WILSON SONSINI GOODRICH & ROSATI
                            Professional Corporation
                               650 Page Mill Road
                        Palo Alto, California 94304-1050

<TABLE>
<CAPTION>
==========================================================================================================================
                                            CALCULATION OF REGISTRATION FEE
==========================================================================================================================
   Title of Securities to be     Amount to be        Proposed Maximum            Proposed Maximum          Amount of
          Registered              Registered    Offering Price Per Share(1) Aggregate Offering Price(1) Registration Fee
--------------------------------------------------------------------------------------------------------------------------
<S>                                <C>                    <C>                        <C>                      <C>
Common Stock,
$.001 par value
Newly reserved under 1997
Employee Stock
Purchase Plan                      1,250,000              68.5625                    85,703,125               23,825
==========================================================================================================================
</TABLE>

--------------------
         (1) The Proposed Maximum Offering Price Per Share was estimated in
accordance with Rule 457(c) and Rule 457(h) under the Securities Act of 1933, as
amended (the "SECURITIES ACT") solely for the purpose of calculating the
registration fee, based on the average between the high and low price of the
Registrant's stock as reported in the Nasdaq National Market System on August
10, 1999.


<PAGE>   2

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

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

         (a)      Registrant's Annual Report on Form 10-K for the fiscal year
                  ended June 30, 1998 (File No. 000-09992) pursuant to Section
                  13(a) of the Securities Exchange Act of 1934, as amended (the
                  "EXCHANGE ACT");

         (b)      Registrant's definitive proxy statement dated October 10,
                  1997, filed in connection with the November 17, 1998 Annual
                  Meeting of Stockholders of the Company;

         (c)      Registrant's Quarterly Report on Form 10-Q for the fiscal
                  quarter ended March 30, 1999, filed pursuant to Section 13(a)
                  of the Exchange Act;

         (d)      Registration Statement on Form S-8 filed with the Securities
                  and Exchange Commission on December 4, 1998 registering shares
                  under the 1997 Employee Stock Purchase Plan (File No.
                  333-68415).

         (e)      The description of the Registrant's Common Stock as set forth
                  in the Registration Statement filed by the Registrant on Form
                  8-A on March 29, 1989 (File No. 000-09992) pursuant to Section
                  12(g) of the Exchange Act and any amendments or reports
                  thereto filed with the Securities and Exchange Commission for
                  the purpose of updating such description including Amendment
                  No. 1 to Form 8-A filed September 25, 1995 and Amendment No. 2
                  to Form 8-A filed September 24, 1996.

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

ITEM 4.  DESCRIPTION OF SECURITIES.

         The class of securities to be offered is registered under Section 12 of
the Exchange Act.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Inapplicable.

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





                                      II-1

<PAGE>   3

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 Company's Amended and Restated Certificate of Incorporation
provides that to the fullest extent permitted by the DGCL, no director of the
Company shall be personally liable to the Company 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 Company's Bylaws provide that the Company shall indemnify to the
full 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 Company.

         The Company 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

         Inapplicable.

ITEM 8.  EXHIBITS

         See Exhibit Index.

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 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.





                                      II-2

<PAGE>   4

                  (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 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to 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.

         (c) 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.





















                                      II-3

<PAGE>   5

                                   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 San Jose, State of California, on August 12, 1999.




                           KLA-TENCOR CORPORATION


                           By: /s/ Robert J. Boehlke
                               ------------------------------------------------
                               Robert J. Boehlke, Executive Vice President and
                               Chief Financial Officer



















                                      II-4

<PAGE>   6

                                POWER OF ATTORNEY


         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Kenneth Levy and Robert J. Boehlke, and
each of them, their true and lawful attorneys and agents, with full power of
substitution, each with power to act alone, to sign and execute on behalf of the
undersigned any amendment or amendments to this Registration Statement on Form
S-8 and to perform any acts necessary in order to file such amendments, and each
of the undersigned does hereby ratify and confirm all that said attorneys and
agents, or their or his or her substitutes, shall do or cause to be done by
virtue hereof. Pursuant to the requirements of the Securities Act of 1933, as
amended, 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>
/s/ Kenneth Levy                            Chairman of the Board and                August 12, 1999
-------------------------------------       Director
Kenneth Levy

/s/ Kenneth L. Schroeder                    President, Chief Executive               August 12, 1999
-------------------------------------       Officer and Director
Kenneth L. Schroeder                        (Principal Executive Officer)

/s/ Robert J. Boehlke                       Executive Vice President and             August 12, 1999
-------------------------------------       Chief Financial Officer (Principal
Robert J. Boehlke                           Financial and Accounting
                                            Officer)

                                            Director                                 August 12, 1999
-------------------------------------
James W. Bagley

/s/ Edward W. Barnholt                      Director                                 August 12, 1999
-------------------------------------
Edward W. Barnholt

/s/ Leo J. Chamberlain                      Director                                 August 12, 1999
-------------------------------------
Leo J. Chamberlain

/s/ Richard J. Elkus, Jr.                   Director                                 August 12, 1999
-------------------------------------
Richard J. Elkus, Jr.

/s/ Dean O. Morton                          Director                                 August 12, 1999
-------------------------------------
Dean O. Morton

/s/ Samuel Rubinovitz                       Director                                 August 12, 1999
-------------------------------------
Samuel Rubinovitz

/s/ Jon D. Tompkins                         Director                                 August 12, 1999
-------------------------------------
Jon D. Tompkins

/s/ Dag Tellefsen                           Director                                 August 12, 1999
-------------------------------------
Dag Tellefsen

/s/ Lida Urbanek                            Director                                 August 12, 1999
-------------------------------------
Lida Urbanek
</TABLE>





                                      II-5

<PAGE>   7

                             KLA-TENCOR CORPORATION

                       REGISTRATION STATEMENT ON FORM S-8

                                INDEX TO EXHIBITS


<TABLE>
<CAPTION>
Exhibit
Number                                Description
-------                               -----------
<S>                     <C>
  4.1*                  Certificate of Incorporation, as amended.

  4.2**                 Bylaws of the Registrant, as amended.

  4.3***                Amended and Restated Rights Agreement dated as of
                        August 30, 1995 between the Registrant and The First
                        National Bank of Boston, as Rights Agent.

  5.1                   Opinion re: legality

 10.12+                 1997 Employee Stock Purchase Plan

 23.1                   Consent of Counsel (included in Exhibit 5.1)

 23.2                   Consent of Independent Accountants

 24.1                   Power of Attorney (see Page II-5)
</TABLE>

----------------------
  *  Incorporated by reference to Exhibit 3.1 to the Registrant's Registration
     Statement on Form S-4, dated March 11, 1997 (Commission File No.
     333-23075).

 **  Incorporated by reference to Exhibit 4.2 to the Registrant's Registration
     Statement on Form S-8, dated May 8, 1997 (Commission File No. 333-26681).

***  Incorporated by reference to the Registrant's report on Form 8-A/A
     Amendment No. 1 to the Registration Statement on Form 8-A (filed September
     24, 1996, Commission File No. 000-9992).

+    Incorporated by reference to Exhibit 10.12 to the Registrant's Registration
     Statement on Form S-8, dated January 30, 1998. (Commission File No.
     333-45271)


                                      II-6
[{"type": "S-8", "sequence": "1", "description": "FORM S-8 (1997 EMPLOYEE STOCK PURCHASE PLAN)", "secsgml_size_bytes": 18977}]
{"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": "333-85121", "film-number": "99687703"}, "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 August 13, 1999
                                                   Registration No. 333-
================================================================================

                       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 No.)

                                 160 Rio Robles
                           San Jose, California 95134
          (Address, including zip code, of principal executive offices)

                        1997 EMPLOYEE STOCK PURCHASE PLAN
                           (Full Titles of the Plans)

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

                                ROBERT J. BOEHLKE
                EXECUTIVE VICE PRESIDENT, CHIEF FINANCIAL OFFICER
                             KLA-TENCOR CORPORATION
                                 160 Rio Robles
                           San Jose, California 95134
                     (Name and address of agent for service)
                                 (408) 434-4200
          (Telephone number, including area code, of agent for service)

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

                                    Copy to:
                             JUDITH M. O'BRIEN, ESQ.
                        WILSON SONSINI GOODRICH & ROSATI
                            Professional Corporation
                               650 Page Mill Road
                        Palo Alto, California 94304-1050
==========================================================================================================================
                                            CALCULATION OF REGISTRATION FEE
==========================================================================================================================
   Title of Securities to be     Amount to be        Proposed Maximum            Proposed Maximum          Amount of
          Registered              Registered    Offering Price Per Share(1) Aggregate Offering Price(1) Registration Fee
--------------------------------------------------------------------------------------------------------------------------
Common Stock,
$.001 par value
Newly reserved under 1997
Employee Stock
Purchase Plan                      1,250,000              68.5625                    85,703,125               23,825
==========================================================================================================================
--------------------
         (1) The Proposed Maximum Offering Price Per Share was estimated in
accordance with Rule 457(c) and Rule 457(h) under the Securities Act of 1933, as
amended (the "SECURITIES ACT") solely for the purpose of calculating the
registration fee, based on the average between the high and low price of the
Registrant's stock as reported in the Nasdaq National Market System on August
10, 1999.
2

                                     PART II

               INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE.

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

         (a)      Registrant's Annual Report on Form 10-K for the fiscal year
                  ended June 30, 1998 (File No. 000-09992) pursuant to Section
                  13(a) of the Securities Exchange Act of 1934, as amended (the
                  "EXCHANGE ACT");

         (b)      Registrant's definitive proxy statement dated October 10,
                  1997, filed in connection with the November 17, 1998 Annual
                  Meeting of Stockholders of the Company;

         (c)      Registrant's Quarterly Report on Form 10-Q for the fiscal
                  quarter ended March 30, 1999, filed pursuant to Section 13(a)
                  of the Exchange Act;

         (d)      Registration Statement on Form S-8 filed with the Securities
                  and Exchange Commission on December 4, 1998 registering shares
                  under the 1997 Employee Stock Purchase Plan (File No.
                  333-68415).

         (e)      The description of the Registrant's Common Stock as set forth
                  in the Registration Statement filed by the Registrant on Form
                  8-A on March 29, 1989 (File No. 000-09992) pursuant to Section
                  12(g) of the Exchange Act and any amendments or reports
                  thereto filed with the Securities and Exchange Commission for
                  the purpose of updating such description including Amendment
                  No. 1 to Form 8-A filed September 25, 1995 and Amendment No. 2
                  to Form 8-A filed September 24, 1996.

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

ITEM 4.  DESCRIPTION OF SECURITIES.

         The class of securities to be offered is registered under Section 12 of
the Exchange Act.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Inapplicable.

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

                                      II-1
3

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 Company's Amended and Restated Certificate of Incorporation
provides that to the fullest extent permitted by the DGCL, no director of the
Company shall be personally liable to the Company 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 Company's Bylaws provide that the Company shall indemnify to the
full 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 Company.

         The Company 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

         Inapplicable.

ITEM 8.  EXHIBITS

         See Exhibit Index.

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 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.

                                      II-2
4

                  (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 (and, where applicable, each filing of an
employee benefit plan's annual report pursuant to 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.

         (c) 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.

                                      II-3
5

                                   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 San Jose, State of California, on August 12, 1999.

                           KLA-TENCOR CORPORATION

                           By: /s/ Robert J. Boehlke
                               ------------------------------------------------
                               Robert J. Boehlke, Executive Vice President and
                               Chief Financial Officer

                                      II-4
6

                                POWER OF ATTORNEY

         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Kenneth Levy and Robert J. Boehlke, and
each of them, their true and lawful attorneys and agents, with full power of
substitution, each with power to act alone, to sign and execute on behalf of the
undersigned any amendment or amendments to this Registration Statement on Form
S-8 and to perform any acts necessary in order to file such amendments, and each
of the undersigned does hereby ratify and confirm all that said attorneys and
agents, or their or his or her substitutes, shall do or cause to be done by
virtue hereof. Pursuant to the requirements of the Securities Act of 1933, as
amended, this Registration Statement has been signed by the following persons in
the capacities and on the dates indicated.
SIGNATURE                                  TITLE                             DATE
             ---------                                  -----                             ----
/s/ Kenneth Levy                            Chairman of the Board and                August 12, 1999
-------------------------------------       Director
Kenneth Levy

/s/ Kenneth L. Schroeder                    President, Chief Executive               August 12, 1999
-------------------------------------       Officer and Director
Kenneth L. Schroeder                        (Principal Executive Officer)

/s/ Robert J. Boehlke                       Executive Vice President and             August 12, 1999
-------------------------------------       Chief Financial Officer (Principal
Robert J. Boehlke                           Financial and Accounting
                                            Officer)

                                            Director                                 August 12, 1999
-------------------------------------
James W. Bagley

/s/ Edward W. Barnholt                      Director                                 August 12, 1999
-------------------------------------
Edward W. Barnholt

/s/ Leo J. Chamberlain                      Director                                 August 12, 1999
-------------------------------------
Leo J. Chamberlain

/s/ Richard J. Elkus, Jr.                   Director                                 August 12, 1999
-------------------------------------
Richard J. Elkus, Jr.

/s/ Dean O. Morton                          Director                                 August 12, 1999
-------------------------------------
Dean O. Morton

/s/ Samuel Rubinovitz                       Director                                 August 12, 1999
-------------------------------------
Samuel Rubinovitz

/s/ Jon D. Tompkins                         Director                                 August 12, 1999
-------------------------------------
Jon D. Tompkins

/s/ Dag Tellefsen                           Director                                 August 12, 1999
-------------------------------------
Dag Tellefsen

/s/ Lida Urbanek                            Director                                 August 12, 1999
-------------------------------------
Lida Urbanek
II-5
7

                             KLA-TENCOR CORPORATION

                       REGISTRATION STATEMENT ON FORM S-8

                                INDEX TO EXHIBITS
Exhibit
Number                                Description
-------                               -----------
4.1*                  Certificate of Incorporation, as amended.

  4.2**                 Bylaws of the Registrant, as amended.

  4.3***                Amended and Restated Rights Agreement dated as of
                        August 30, 1995 between the Registrant and The First
                        National Bank of Boston, as Rights Agent.

  5.1                   Opinion re: legality

 10.12+                 1997 Employee Stock Purchase Plan

 23.1                   Consent of Counsel (included in Exhibit 5.1)

 23.2                   Consent of Independent Accountants

 24.1                   Power of Attorney (see Page II-5)
----------------------
  *  Incorporated by reference to Exhibit 3.1 to the Registrant's Registration
     Statement on Form S-4, dated March 11, 1997 (Commission File No.
     333-23075).

 **  Incorporated by reference to Exhibit 4.2 to the Registrant's Registration
     Statement on Form S-8, dated May 8, 1997 (Commission File No. 333-26681).

***  Incorporated by reference to the Registrant's report on Form 8-A/A
     Amendment No. 1 to the Registration Statement on Form 8-A (filed September
     24, 1996, Commission File No. 000-9992).

+    Incorporated by reference to Exhibit 10.12 to the Registrant's Registration
     Statement on Form S-8, dated January 30, 1998. (Commission File No.
     333-45271)

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