<PAGE>

                                 UNITED STATES
                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C. 20549

                                   FORM 10-K/A

(Mark One)
[X]  Annual Report Pursuant to Section 13 or 15(d) of the Securities Exchange
     Act of 1934.

                     For the year ended December 31, 1999
                                      or

[ ]  Transition Report Pursuant to Section 13 or 15(d) of the Securities
     Exchange Act of 1934.

          For the transition period from ____________ to____________.

                     Commission File Number ( 000-25865 )

                        Copper Mountain Networks, Inc.

            (Exact name of registrant as specified in its charter)

            Delaware                                     33-0702004
(State or other jurisdiction of                      (I.R.S. Employer
 incorporation or organization)                     Identification No.)


              2470 Embarcadero Way, Palo Alto, California 94303
                                (650) 687-3300
  (Address, including zip code, and telephone number, including area code, of
                         principal executive offices)

          Securities registered pursuant to Section 12(b) of the Act:
                                     None

          Securities registered pursuant to Section 12(g) of the Act:
                         Common Stock, $.001 par value

     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to such
filing requirements for the past 90 days.     Yes   X   No _____
                                                   ----

     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K.  [ ]

     The aggregate market value of the voting stock held by non-affiliates of
the registrant, as of January 31, 2000 was approximately $2,118,985,000 (based
on the closing price for shares of the registrant's Common Stock as reported by
the Nasdaq National Market for the last trading day prior to that date).
Shares of Common Stock held by each officer, director and holder of 5% or more
of the outstanding Common Stock have been excluded in that such persons may be
deemed affiliates.  This determination of affiliate status is not necessarily a
conclusive determination for other purposes.

The number of shares outstanding of the registrant's Common Stock, $.001 par
value, as of January 31, 2000 was 47,870,942.
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                                    PART IV

   Item 14.  Exhibits, Financial Statement Schedules and Reports on Form 8-K

                                                                          Page
                                                                         Number
                                                                        --------
          (a)  Documents filed as part of the report:
               (1)     Report of Ernst & Young LLP,  Independent
                       Auditors                                            F-1
                       Balance Sheets at December 31, 1999 and 1998        F-2
                       Statements of Operations for 1999, 1998 and
                        1997                                               F-3
                       Statements of Stockholders' Equity for 1999,
                        1998 and 1997                                      F-4
                       Statements of Cash Flows for 1999, 1998 and
                       1997                                                F-6
                       Notes to Financial Statements                       F-7
                       Schedule II Valuation and Qualifying Accounts      II-1

          All other schedules for which provision is made in the applicable
     accounting regulation of the Securities and Exchange Commission are not
     required under the related instructions or are inapplicable and therefore
     have been omitted.

               (2)  Exhibits

 Exhibit
 Number                                  Description of Document
 ------                                  -----------------------
    3.1        Amended and Restated Certificate of Incorporation.(1)
    3.2        Bylaws.(1)
    4.1        Reference is made to Exhibits 3.1 and 3.2.(1)
    4.2        Specimen Stock Certificate.(1)
   10.1        Amended and Restated 1996 Equity Incentive Plan (the "1996
               Plan").(1)
   10.2        Form of Stock Option Agreement pursuant to the 1996 Plan.(1)
   10.3        1999 Employee Stock Purchase Plan and related offering
               documents.(1)
   10.4        Employment Agreement between the Company and Steve Hunt, dated
               July 31, 1996.(1)
   10.5        Employment Agreement between the Company and Richard Gilbert,
               dated March 22, 1998.(1)
   10.6        Master Equipment Lease between the Company and Comdisco, Inc.,
               dated September 30, 1997.(1)
   10.7        Loan and Security Agreement between the Company and Silicon
               Valley Bank, dated August 14, 1998.(1)
   10.8        Loan and Security Agreement between the Company and Silicon
               Valley Bank and MMC/GATX Partnership No. 1, dated October 4,
               1996.(1)
   10.9        Office Lease between the Company and Public Storage Properties
               XVIII, Inc., dated June 14, 1996.(1)
  10.10        Office Lease between the Company and R.G. Harris & Company, dated
               August 12, 1997.(1)
  10.11        Office Sublease between the Company and Stuart Leeb and
               Associates, dated May 1, 1998.(1)
  10.12        Office Lease between the Company and Palomar Enterprises, Inc.,
               dated July 20, 1998.(1)
  10.13        Warrant Agreement between the Company and MMC/GATX Partnership
               No. 1, dated October 4, 1996.(1)
  10.14        Warrant Agreement between the Company and Silicon Valley Bank,
               dated October 4, 1996.(1)
  10.15        Warrant Agreement between the Company and Comdisco, Inc., dated
               October 29, 1997.(1)

                                       1
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 Exhibit
 Number                                  Description of Document
 ------                                  -----------------------
  10.16        Warrant Agreement between the Company and Comdisco, Inc., dated
               April 27, 1998.(1)
  10.17        Warrant Agreement between the Company and Intel Corporation,
               dated January 14, 1997.(1)
  10.18        Warrant Agreement between the Company and Silicon Valley Bank,
               dated August 14, 1998.(1)
  10.19        Amended and Restated Investors' Rights Agreement by and among the
               Company and certain stockholders of the Company, dated October 9,
               1998.(1)
  10.20        Right of First Refusal and Co-Sale Agreement by and among the
               Company and certain stockholders of the Company, dated October 9,
               1998.(1)
  10.21        Voting Agreement by and among the Company and certain
               stockholders of the Company, dated October 9, 1998.(1)
  10.22        Founder Stock Purchase Agreement between the Company and Joseph
               D. Markee, dated March 11, 1996.(1)
  10.23        First Amendment to Founder Stock Purchase Agreement between the
               Company and Joseph D. Markee, dated June 12, 1998.(1)
  10.24        Founder Stock Purchase Agreement between the Company and Mark J.
               Handzel, dated March 11, 1996.(1)
  10.25        First Amendment to Founder Stock Purchase Agreement between the
               Company and Mark J. Handzel, dated January 27, 1999.(1)
 +10.26        General Agreement for the Procurement of Products and Services
               and the Licensing of Software between the Company and Lucent
               Technologies Inc., dated November 17, 1998.(1)
 +10.27        OEM Purchase and Development Agreement between the Company an
               3COM Corporation, dated November 24, 1998.(1)
 +10.28        Development, Manufacturing and Supply Agreement between the
               Company and Netopia, Inc., dated May 19, 1998.(1)
  10.29        Warrant Agreement between the Company and Intel Corporation,
               dated January 14, 1997.(1)
  10.30        1999 Non-Employee Directors' Stock Option Plan.(1)
  10.31        Form of Nonqualified Stock Option for use with 1999 Non-Employee
               Directors' Stock Option Plan.(1)
  10.32        Form of Indemnification Agreement(1)
 +10.33        Equipment Purchase Agreement between the Company and NorthPoint
               Communications, Inc. dated April 8, 1999.(1)
 +10.34        Standard Full Service Gross Office Lease among the Company,
               Pacific Sorrento Mesa Holdings, L.P., and Pacific Stonecrest
               Holdings, L.P., dated March 31, 1999.(1)
 +10.35        Equipment Purchase Agreement between the Company and NorthPoint
               Communications, Inc. dated July 21, 1999.(2)
 +10.36        Equipment Purchase Agreement between the Company and Rhythms
               NetConnections, Inc. dated December 10, 1999.
  10.37        Software License Agreement between the Company and Rhythms
               NetConnections, Inc. dated December 10, 1999.*
 +10.38        Customer Technical Support Services Agreement between the Company
               and Rhythms NetConnections, Inc. dated December 10, 1999.
  10.39        Employment Agreement between the Company and Joseph D. Markee,
               dated March 12, 1999.(1)
   23.1        Consent of Ernst & Young LLP, Independent Auditors.*
   27          Financial Data Schedule.*

     ___________________________________________________________________________
      *   Previously filed with the Registrant's Annual Report on Form 10-K for
          the year ended December 31, 1999, filed on March 17, 2000.

     (1)  Filed as an exhibit to the Registrant's Registration Statement on Form
          S-1 filed with the Securities and Exchange Commission (the
          "Commission") on March 1, 1999 (File No. 333-73153), as amended by
          Amendment No. 1 filed with the Commission on April 13, 1999, Amendment
          No. 2 filed with the Commission on April 26, 1999, and Amendment No. 3
          filed with the Commission on

                                       2
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          May 11, 1999.
     (2)  Filed as an exhibit to the Registrant's Quarterly Report on Form 10-Q
          for the quarter ended September 30, 1999.
     +    Confidential treatment has been requested with respect to certain
          portions of this exhibit. Omitted portions have been filed separately
          with the Securities and Exchange Commission.

                                       3
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                                  SIGNATURES

  Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange
Act of 1934, the registrant has duly caused this report to be signed on its
behalf by the undersigned, thereunto duly authorized.

Date:  April 20, 2000


                                        Copper Mountain Networks, Inc.

                                        By: /s/ RICHARD S. GILBERT
                                            ------------------------------
                                            Richard S.  Gilbert
                                            President and Chief Executive
                                            Officer

Pursuant to the requirements of the Securities Exchange Act of 1934, this report
has been signed below by the following persons on behalf of the registrant and
in the capacities and on the dates indicated.

          Signature                     Title                         Date
          ---------                     -----                         ----

/s/ RICHARD S. GILBERT        President, Chief Executive          April 20, 2000
-----------------------------
Richard S. Gilbert            Officer and Director (Principal
                              Executive Officer)

/s/ JOHN A. CREELMAN          Vice President of Finance, Chief    April 20, 2000
-----------------------------
John A. Creelman              Financial Officer and Secretary
                              (Principal Financial Officer and
                              Principal Accounting Officer)

/s/ JOSEPH D. MARKEE          Chief Technical Officer and         April 20, 2000
-----------------------------
Joseph D. Markee              Chairman of the Board

/s/ ROBERT L. BAILEY          Director                            April 20, 2000
-----------------------------
Robert L. Bailey


/s/ TENCH COXE                Director                            April 20, 2000
-----------------------------
Tench Coxe

/s/ ROGER EVANS               Director                            April 20, 2000
-----------------------------
Roger Evans

/s/ RICHARD H. KIMBALL        Director                            April 20, 2000
-----------------------------
Richard H. Kimball

/s/ RAYMOND V. THOMAS         Director                            April 20, 2000
-----------------------------
Raymond V. Thomas

/s/ ANDREW W. VERHALEN        Director                            April 20, 2000
-----------------------------
Andrew W. Verhalen

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