Exhibit 99.1

      CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER
           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 Annual
Report of Komag, Incorporated on Form 10-K for the fiscal year ended December
29, 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-K
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, Kathleen A. Bayless, 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 Komag, Incorporated on Form 10-K for the fiscal year ended December
29, 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-K
fairly presents in all material respects the financial condition and results of
operations of Komag, Incorporated.

                                        By:    /S/ Kathleen A. Bayless
                                           -------------------------------
                                        Name: Kathleen A. Bayless
                                        Title: Chief Financial Officer