EXHIBIT 5.1.2


                                December __, 2003

Komag, Incorporated
1710 Automation Parkway
San Jose, CA 95131

Ladies and Gentlemen:


      We have examined the Registration Statement on Form S-3 filed by Komag,
Incorporated (the "Company") with the Securities and Exchange Commission (the
"Commission") on November 3, 2003, as amended by Amendment No. 1 thereto filed
with the Commission on December 9, 2003 (such registration statement, as so
amended, herein the "Registration Statement"), in connection with the
registration under the Securities Act of 1933, as amended (the "Act"), of up to
$80,500,000 aggregate principal amount of the Company's Convertible Subordinated
Notes due 2023 (including up to $10,500,000 aggregate principal amount subject
to an over-allotment option to be granted to the underwriters) (the "Notes") and
the Company's common stock, $0.01 par value, into which the Notes may be
converted (the "Conversion Shares") pursuant to the terms of the Notes and the
indenture in substantially the form filed as an exhibit to the Registration
Statement (the "Indenture"), to be entered into by the Company and U.S. Bank
National Association, as trustee thereunder (the "Trustee"). The Notes are to be
issued pursuant to the Indenture and sold pursuant to an underwriting agreement
(the "Underwriting Agreement") in substantially the form filed as an exhibit to
the Registration Statement.


      We have reviewed such corporate records, certificates and other documents,
and such questions of law, as we have considered necessary or appropriate for
the purposes of this opinion. We have assumed that all signatures are genuine,
that all documents submitted to us as originals are authentic, that all copies
of documents submitted to us conform to the originals, and that the Notes will
be duly authenticated by the Trustee for the Notes as provided in the Indenture
for the Notes.

      We have relied as to certain matters on information obtained from public
officials, officers of the Company, and other sources believed by us to be
responsible.

      Based upon the foregoing, and subject to the qualifications set forth
below, we are of the opinion that:

            1.    The Notes have been duly authorized and, when executed and
                  delivered in accordance with the Indenture and sold and
                  delivered pursuant to the Underwriting Agreement, will be
                  valid and binding obligations of the Company, enforceable
                  against the Company in accordance with their terms, subject to
                  bankruptcy, insolvency, fraudulent transfer, reorganization,
                  moratorium and other laws of general applicability relating to
                  or affecting creditors' rights and to general equity
                  principles (regardless of whether enforceability is considered
                  at law or in equity).

            2.    The Conversion Shares have been duly authorized and, when
                  issued upon such conversion in accordance with the terms of
                  the Notes and the Indenture, will be validly issued, fully
                  paid and nonassessable.

      The foregoing opinion is subject to the qualifications that we express no
opinion as to (i) waivers of defenses or statutory or constitutional rights or
waivers of unmatured claims or rights, (ii) rights to indemnification,
contribution or exculpation to the extent that they purport to indemnify any
party against, or release or limit any party's liability for, its own breach or
failure to comply with statutory obligations, or to the extent such provisions
are contrary to public policy, or (iii) rights to collection or liquidated
damages or penalties on overdue or defaulted obligations.

      We are members of the bar of the State of New York. We do not purport to
be experts in, and do not express any opinion on, any laws other than the law of
the State of New York, the Delaware General Corporation Law and the Federal laws
of the United States of America.

      We hereby consent to the filing of this opinion as Exhibit 5.1.2 to the
above-referenced Registration Statement and to the use of our name under the
caption "Legal Matters" in the Registration Statement and the prospectus
included therein.

                                          Very truly yours,

                                          WILSON SONSINI GOODRICH & ROSATI
                                          Professional Corporation