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                         [COOLEY GODWARD LLP LETTERHEAD]



                                                                     Exhibit 5.1


November 4, 1999

HMT Technology Corporation
1055 Page Avenue
Fremont, CA 94538

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by HMT Technology Corporation (the "Company") of a Registration
Statement on Form S-8 (the "Registration Statement") with the Securities and
Exchange Commission covering the offering of 1,500,000 shares of the Company's
Common Stock, $0.001 par value (the "Shares"), pursuant to the Company's
Employee Stock Purchase Plan (the "Plan").

In connection with this opinion, we have examined the Registration Statement and
related Prospectus, your Certificate of Incorporation and By-laws, as amended,
and such other documents, records, certificates, memoranda and other instruments
as we deem necessary as a basis for this opinion. We have assumed the
genuineness and authenticity of all documents submitted to us as originals, the
conformity to originals of all documents submitted to us as copies thereof, and
the due execution and delivery of all documents where due execution and delivery
are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion
that the Shares, when sold and issued in accordance with the Plan, the
Registration Statement and related Prospectus, will be validly issued, fully
paid, and nonassessable.

We consent to the filing of this opinion as an exhibit to the Registration
Statement.

Very truly yours,

Cooley Godward LLP


/s/ James C. Kitch