Document:

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                                                                EXHIBIT 10.37(b)

                        [ALTERA CORPORATION LETTERHEAD]

May 22, 1997

Mr. Hiroto Nakamura
Department General Manager
IC Sales Dept. 1
International Sales & Marketing Group
-IC/Electronic Components
Sharp Corporation
2613-1 Ichinomoto-cho
Tenri City, Nara 632 Japan

RE: Amendment of Products Supply Agreement

Dear Mr. Nakamura:

     Altera Corporation ("Altera") and Sharp Corporation ("Sharp") have
entered into the LSI Products Supply Agreement dated October 1, 1993, as
amended by Mr. Rodney Smith's letter addressed to Mr. Tadahiko Ishino on
August 28, 1996, (the "Supply Agreement") pursuant to which Altera purchases
from Sharp products manufactured by Sharp, which Altera resells worldwide
under the Altera name. As we have previously discussed with you, Altera has
established an indirect, wholly-owned subsidiary, Altera International
Limited, a corporation organized under the laws of Hong Kong ("AIL"), which
desires to purchase products manufactured by Sharp under the Supply Agreement
for resale under the Altera name. The purpose of this letter is to formally
memorialize our prior discussions in which Sharp has agreed to accept purchase
orders submitted by AIL.

                       AMENDMENT OF THE SUPPLY AGREEMENT

     Altera desires to amend the Supply Agreement to permit AIL to take all
actions permitted to be taken by Altera under the Supply Agreement. Sharp is
willing to amend the Supply Agreement as requested by Altera, provided Altera
guarantees the performance of AIL of its obligations under the Supply Agreement
and agrees to indemnify Sharp against any loss or damage which it might suffer
as a result of accepting instructions and orders from AIL under the Supply
agreement. The purpose of this letter agreement (the "Amendment") is to amend
the Supply Agreement, effective as of the date of acceptance of the Amendment by
Sharp (the "Effective Date"), to effectuate these changes. Capitalized terms not
otherwise defined in this Amendment have the meaning given to them in the Supply
Agreement.

     1. As of the Effective Date, Sharp agrees to accept order of PRODUCTS from
        AIL under the Supply Agreement. With respect to and PRODUCTS ordered by
        AIL, AIL shall be responsible for all actions required or permitted to
        be taken by Altera under Articles 2, 3, 4, 6, 7, 8, 9, 12, 14, 15, 17,
        and 20 of the Supply Agreement. Sharp agrees to accept orders for
        PRODUCTS and requests for services from AIL in accordance with the terms
        of Articles 2, 3, 4, 6, 7, 8, 9, 12, 14, 15, 17, and 20 of the Supply
        Agreement.

     2. All Altera inventory purchase order that are outstanding as of the close
        of business on June 30, 1997 will be assumed by and transferred to AIL.
        Sharp agrees to make all shipments under these purchase orders to AIL
        pursuant to Article 3 of the Supply Agreement.
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3.  AIL shall make payments to Sharp, in accordance with the provisions of
    Article 5 of the Supply agreement as amended by the letter dated August 20,
    1996, and accepted by Sharp on August 28, 1996, for all PRODUCTS ordered by
    AIL. Until such time as AIL establishes an irrevocable standby letter of
    credit acceptable to and in favor of Sharp as required under the said
    letter amendment, Altera shall cause its existing letter of credit with
    Banque Nationale de Paris to provide for acceptance of Sharp drafts with
    respect to orders for PRODUCTS made by AIL.

4.  Altera guarantees to Sharp and the successors, transferees and assigns of
    Sharp permitted under the Supply Agreement, the prompt performance by AIL
    of all of its obligations under the Supply Agreement, as amended by this
    Agreement.

5.  This Amendment shall be governed by and construed and enforced in
    accordance with the laws of the State of California of the United States of
    America, excluding its conflicts of laws provisions.

6.  Each of the parties to this Amendment hereby confirms in all other respects
    the Supply Agreement.

7.  This Amendment may be executed in one or more counterparts, each of which
    shall be an original and all of which together shall be but one agreement.

    If the above provisions accurately and completely reflect the parties'
understanding of the arrangements described, please so indicate by executing
and returning to Altera the enclosed copy of the Amendment.

Very truly yours,

ALTERA CORPORATION

By:    /s/ RODNEY SMITH
Name:  Rodney Smith
Title: President and Chief Executive Officer
       Altera Corporation

ALTERA INTERNATIONAL LIMITED

By:    /s/ NATHAN SARKISIAN
Name:  Nathan Sarkisian
Title: Director, Altera International Limited

The foregoing is agreed to and accepted by Sharp Corporation this 24th day of
June, 1997.

SHARP CORPORATION

By:    /s/ TADAHIKO ISHINO
Name:  Tadahiko Ishino
Title: Executive Director and Group General Manager
       International Sales and Marketing Group
       Sharp Corporation<PAGE>   1
                                                                EXHIBIT 10.37(c)
                        [ALTERA CORPORATION LETTERHEAD]

May 22, 1998

Mr. Hiroto Nakamura
Department General Manager
North & South America III, Sales & Marketing Group
Electronics Components and Devices
SHARP CORPORATION
2613-1 Ichinomoto-cho
Tenri, Nara 632
Japan

SUBJECT: AMENDMENT OF PRODUCTS SUPPLY AGREEMENT

Dear Hiro:

Altera Corporation ("Altera") and Sharp Corporation ("Sharp") have entered into
the LSI Products Supply Agreement dated October 1, 1993, as amended by Mr.
Rodney Smith's letter addressed to Mr. Tadahiko Ishino on August 28, 1996, and
as further amended by the letter addressed to you on May 22, 1997 (the "Supply
Agreement"). This letter will memorialize the understanding reached between
Sharp and Altera to revise the terms of payment set forth in the Supply
Agreement and the August 28, 1996, letter amendment.

Article 5, Paragraph (b) of the Supply Agreement provides for payment pursuant
to a letter of credit ("LC") payable at sight. We have agreed that instead of
these payment terms, Sharp will invoice Altera for wafer purchases on shipment,
with net thirty (30) day payment terms. Altera will open an irrevocable standby
LC in favor of Sharp at a mutually acceptable bank, presently Banque Nationale
de Paris, to back up Altera's payment obligations. The amount of the standby LC
will be as agreed upon by Sharp and Altera from time to time, and will be four
hundred seventy-five million (475,000,000) yen for the period August 20, 1998,
to August 19, 1999. This amount may be adjusted if there is a material and
sustained change in wafer volumes in the first and second quarters of 1999.
Sharp has agreed to give Altera written notice of any invoices not paid within
thirty (30) days, and to only draw on the LC if and to the extent that the
invoice remains unpaid after 15 days have passed since delivery of notice.

If the above provisions accurately and completely reflect the parties'
understanding of the arrangements described, please so indicate by executing and
returning to Altera a signed copy of this letter.

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Mr. Hiroto Nakamura
May 22, 1998
Page 2

Thank you for your cooperation.

Sincerely,

/s/ DENIS BERLAN
---------------------------
Denis Berlan
Executive Vice President and Chief Operating Officer
Altera Corporation

The foregoing is agreed to and accepted by Sharp Corporation this 8th day of
July 1998.

SHARP CORPORATION
By:

/s/ HIROTO NAKAMURA
--------------------
Hiroto Nakamura
Department General Manager
Sharp Corporation<PAGE>   1
                                                               EXHIBIT 10.42 (a)
                        [ALTERA CORPORATION LETTERHEAD]

May 16, 1997

Taiwan Semiconductor Manufacturing Co., Ltd.
1740 Technology Drive, suite 660
San Jose, CA 95110
Attention: Loretta Liang

Taiwan Semiconductor Manufacturing Co., Ltd.
121 Park Avenue 3, Science-Based Industrial Park
Hsinchu, Taiwan, ROC

RE: Amendment of Wafer Supply Agreement

Ladies and Gentlemen:

     Altera Corporation ("Altera") and Taiwan Semiconductor Manufacturing Co.,
Ltd. ("TSMC") have entered into the Wafer Supply Agreement dated June 26, 1995
(the "Supply Agreement") pursuant to which Altera purchases from TSMC products
manufactured by TSMC, which Altera resells worldwide under the Altera name. As
we have previously discussed with you, Altera has established an indirect,
wholly-owned subsidiary, Altera International Limited, a corporation organized
under the laws of Hong Kong ("AIL"), which desires to purchase products
manufactured by TSMC under the Supply Agreement for resale under the Altera
name. The purpose of this letter is to formally memorialize our prior
discussions in which TSMC has agreed to accept purchase orders submitted by AIL.

                         AMENDMENT OF SUPPLY AGREEMENT

     Altera desires to amend the Supply Agreement to permit AIL to take all
actions permitted to be taken by Altera under the Supply Agreement, except as
provided in this letter agreement. TSMC is willing to amend the Supply Agreement
as requested by Altera, provided Altera guarantees the performance of AIL of its
obligations under the Supply Agreement. The purpose of this letter agreement
(the "Amendment") is to amend the Supply Agreement, effective as of the date of
acceptance of the Amendment by TSMC (the "Effective Date"), to effectuate these
changes. Capitalized terms not otherwise defined in this Amendment have the
meaning given to them in the Supply Agreement.

     1. As of the Effective Date, TSMC agrees to accept order of Wafers and
        Devices from AIL under the Supply Agreement. With respect to any Wafers
        and Devices ordered by AIL, AIL shall be responsible for all actions
        required or permitted to be taken by Altera under Articles 2, 3, 4, 6,
        7, 9, 11, 12, 13, 14, 15, 16, 19 and 20 of the Supply Agreement. TSMC
        agrees to accept orders for Wafers and Devices and requests for services
        from AIL in accordance with the terms of Articles 2, 3, 4, 6, 7, 9, 11,
        12, 13, 14, 15, 16, 19 and 20 of the Supply Agreement.
<PAGE>   2
     2.   All Altera inventory purchase orders that are outstanding as of the
close of business on May 23, 1997 will be assumed by and transferred to AIL.
TSMC agrees to make all shipments under these purchase orders to AIL, pursuant
to Article 15 of the Supply Agreement.

     3.   AIL shall make payments to TSMC in accordance with the provisions of
Article 8 of the Supply Agreement for all Wafers and Devices ordered by AIL.

     4.   Altera guarantees to TSMC and the successors, transferees and assigns
of TSMC permitted under the Supply Agreement, the prompt performance by AIL of
all of its obligations under the Supply Agreement, as amended by this Amendment.

     5.   This Amendment shall be governed by and construed and enforced in
accordance with the laws of the State of California of the United States of
America, excluding its conflicts of laws provisions.

     6.   This Amendment may be executed in one or more counterparts, each of
which shall be an original and all of which together shall be but one agreement.

     If the above provisions accurately and completely reflect the parties'
understanding of the arrangements described, please so indicate by executing and
returning to Altera the enclosed copy of the Amendment.

Very truly yours,

ALTERA CORPORATION

By:  /s/ MOHAMMED DHAKNI
    -----------------------------
Name:  Mohammed Dhakni
Title: Manager Purchasing

ALTERA INTERNATIONAL LIMITED

By:  /s/ C. WENDELL BERGERE
    -----------------------------
Name:  C. Wendell Bergere
Title: Director, Altera International Limited

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The foregoing is agreed to and
accepted this 1 day of June, 1997

TAIWAN SEMICONDUCTOR MANUFACTURING CO., LTD.

By:       /s/ MORRIS CHANG

Name:     Morris Chang

Title:    Chairman and President

Address:  121 Park Avenue 3
          Science-Based Industrial Park
          Hsinchu, Taiwan, ROC

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