EXHIBIT 5.1

October 26, 2000

Applied Micro Circuits Corporation
6290 Sequence Drive
San Diego, CA  92121

Re:    Registration Statement on Form S-8

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection
with the filing by Applied Micro Circuits Corporation (the "Company") of a
Registration Statement on Form S-8 (the "Registration Statement") with the
Securities and Exchange Commission, covering the offering of up to 4,176,319
shares of the Company's Common Stock, $.01 par value (the "Shares"), issuable
upon the exercise of outstanding options granted pursuant to the MMC Networks,
Inc. 1993 Stock Plan, 1997 Stock Plan, 1997 Director Option Plan and 1997
Employee Stock Purchase Plan (collectively the "Plans"). Such options were
assumed by the Company in connection with the Agreement and Plan of Merger and
Reorganization dated as of August 28, 2000 (the "Merger Agreement"), by and
among the Company, Mercury Acquisition Corp. and MMC Networks, Inc.

In connection with this opinion, we have examined and relied upon the
Registration Statement and related prospectus, the Plans, the form of option
agreements under the Plans, the Merger Agreement, the Company's Certificate of
Incorporation and Bylaws, as amended, and the originals or copies certified to
our satisfaction of such records, documents, certificates, memoranda and other
instruments as in our judgment are necessary or appropriate to enable us to
render the opinion expressed below. 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 Plans, the assumed
option agreements, the Registration Statement and related prospectus, will be
validly issued, fully paid, and nonassessable (except as to shares issued
pursuant to certain deferred payment arrangements, which will be fully paid and
nonassessable when such deferred payments are made in full).

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

Very truly yours,

Cooley Godward LLP

/s/ D. BRADLEY PECK
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D. Bradley Peck