EXHIBIT 5.1

               [FORM OF WILSON SONSINI GOODRICH & ROSATI OPINION]

                [LETTERHEAD OF WILSON SONSINI GOODRICH & ROSATI]


                                October 31, 2003

Komag, Incorporated
1710 Automation Parkway
San Jose, California  95131

        Re:  Registration Statement on Form S-1

Ladies and Gentlemen:

        We have examined the Post Effective Amendment Registration Statement to
Form S-1 on Form S-3 filed by Komag, Incorporated (the "Company") with the
Securities and Exchange Commission on October 17, 2003 (the "Registration
Statement") in connection with the registration under the Securities Act of
1933, as amended, of up to 9,981,609 shares of the Company's common stock (the
"Shares") and $ 83,711,896.16 in aggregate principal amount plus pay-in-kind
interest of the Company's Senior Secured Notes due 2007 (the "Senior Notes").
The Shares and the Senior Notes are being registered for resale to the public by
the selling security holders as described in the Registration Statement. As
legal counsel of the Company, we have examined the proceedings proposed to be
taken in connection with the registration of the Shares and the Senior Notes.

        Based upon the foregoing, we are of the opinion that (i) the Shares,
when sold in the manner described in the Registration Statement, will be duly
authorized, validly issued, fully paid and nonassessable and (ii) the Senior
Notes have been duly authorized and are binding obligations of the Company
entitled to the benefits of the Indenture, dated as of June 30, 2002, between
the Company and the Bank of New York, as Trustee (the "Indenture").

        Our opinions set forth herein are qualified as to: (i) limitations
imposed by bankruptcy, insolvency, reorganization, arrangement, fraudulent
conveyance, moratorium or other similar laws relating to or affecting the rights
of creditors generally, including, without limitation, laws relating to
fraudulent transfers or conveyances and preferences, (ii) rights to
indemnification and contribution which may be limited by applicable law or
equitable principles, and (iii) the effect of general principles of equity,
including without limitation, concepts of materiality, reasonableness, good
faith and fair dealing, and the possible unavailability of specific performance,
injunctive relief or other equitable relief, and limitations on rights of
acceleration regardless of whether considered in a proceeding in equity or at
law.

        To the extent that the obligations of the Company under the Indenture
may be dependent upon such matters, we assume for purposes of this opinion that
the Trustee under the Indenture has been duly organized, is validly existing and
is in good standing under the laws of its jurisdiction of organization; that the
Trustee is duly qualified to engage in the activities contemplated by the
Indenture; that the Indenture has been duly authorized, executed and delivered
by the Trustee and constitutes a legally valid, binding and enforceable
obligation of the Trustee enforceable against the Trustee in accordance with its
terms; that the Trustee is in compliance, generally and with respect to acting
as trustee under the Indenture, with all applicable laws and regulations; and
that the Trustee has the requisite organizational and legal power and authority
to perform its obligations under the Indenture.

        We consent to the use of this opinion as an exhibit to the Registration
Statement, and further consent to the use of our name wherever appearing in the
Registration Statement, including the prospectus constituting a part thereof,
and any amendment thereto.

                                    Very truly yours,
                                    WILSON SONSINI GOODRICH & ROSATI
                                    Professional Corporation
                                    /s/ Wilson Sousini Goodrich & Rosati