Exhibit 99.1

      CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND 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, Thian Hoo Tan, certify, pursuant to 18 U.S.C. Section 1350, as adopted
pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly
Report of Komag, Incorporated on Form 10-Q for the quarterly period ended June
30, 2002 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 Form 10-Q
fairly presents in all material respects the financial condition and results of
operations of Komag, Incorporated.

                                            By:   /S/ Thian Hoo Tan
                                               ---------------------------------
                                            Name: Thian Hoo Tan
                                            Title:   Chief Executive Officer

I, Edward H. Siegler, certify, pursuant to 18 U.S.C. Section 1350, as adopted
pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that the Quarterly
Report of Komag, Incorporated on Form 10-Q for the quarterly period ended June
30, 2002 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 10-Q
fairly presents in all material respects the financial condition and results of
operations of Komag, Incorporated.

                                            By:    /S/ Edward H. Siegler
                                               ---------------------------------
                                            Name: Edward H. Siegler
                                            Title:   Chief Financial Officer