Exhibit 32.1

                                     CERTIFICATION OF CHIEF EXECUTIVE OFFICER
                                                       PURSUANT TO
                                                18 U.S.C. SECTION 1350,
                                                AS ADOPTED PURSUANT TO
                                   SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



I, Kenneth L. Schroeder, certify, pursuant to 18 U.S.C. Section 1350, as adopted
pursuant  to  Section  906 of the  Sarbanes-Oxley  Act of 2002,  that the Annual
Report of KLA-Tencor  Corporation  on Form 10-K/A for the fiscal year ended June
30, 2003 fully complies with the  requirements  of Section 13(a) or 15(d) of the
Securities  Exchange Act of 1934 and that  information  contained in such Annual
Report on Form 10-K/A  fairly  presents in all material  respects the  financial
condition and results of operations of KLA-Tencor Corporation.

September 29, 2003                            By:   /s/  Kenneth L. Schroeder

Dated                                              Name: Kenneth L. Schroeder
                                               Title:   Chief Executive Officer



                                     CERTIFICATION OF CHIEF FINANCIAL OFFICER
                                                     PURSUANT TO
                                               18 U.S.C. SECTION 1350,
                                               AS ADOPTED PURSUANT TO
                                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002



I, John H.  Kispert,  certify,  pursuant to 18 U.S.C.  Section  1350, as adopted
pursuant  to  Section  906 of the  Sarbanes-Oxley  Act of 2002,  that the Annual
Report of KLA-Tencor  Corporation  on Form 10-K/A for the fiscal year ended June
30, 2003 fully complies with the  requirements  of Section 13(a) or 15(d) of the
Securities  Exchange Act of 1934 and that  information  contained in such Annual
Report on Form 10-K/A  fairly  presents in all material  respects the  financial
condition and results of operations of KLA-Tencor Corporation.

September 29, 2003                                  By:   /s/  John H. Kispert

Dated                                                    Name:  John H. Kispert
                                               Title:   Chief Financial Officer

A signed  original of this written  statement  required by Section 906  has been
provided  to  KLA-Tencor   Corporation   and  will  be  retained  by  KLA-Tencor
Corporation and furnished to the Securities and Exchange Commission or its staff
upon request.