<PAGE>

                                                                    EXHIBIT 10.8

                                                                  EXECUTION COPY

                                SEVENTH AMENDMENT

                  SEVENTH AMENDMENT, dated as of June 16, 2003 (this
"Amendment"), to the Second Amended and Restated Credit Agreement, dated as of
May 23, 2000 (as amended, the "Credit Agreement"), among CALPINE CORPORATION, a
Delaware corporation (the "Borrower"), the various financial institutions as are
or may become parties thereto (the "Lenders") and THE BANK OF NOVA SCOTIA, as
administrative agent (in such capacity, the "Agent").

                  WHEREAS pursuant to the Credit Agreement, the Lenders have
made extensions of credit to the Borrower; and

                  WHEREAS the Borrower has requested that a provision of the
Credit Agreement be modified in the manner provided for in this Amendment, and
the Lenders are willing to agree to such modification as provided for in this
Amendment.

                  NOW, THEREFORE, the parties hereto hereby agree as follows:

                  1. Defined Terms. Capitalized terms used and not defined
herein shall have the meanings given to them in the Credit Agreement, as amended
hereby.

                  2. Amendment to Credit Agreement. The definition of
"Commitment Termination Date" in Section 1.1 of the Credit Agreement is hereby
amended by deleting clause (a) thereof in its entirety and by substituting in
lieu thereof the following: "(a) July 16, 2003;"; provided, that if, by 5:00
p.m. (New York time) on June 24, 2003, the Agent shall not have received a
consent letter, in form and substance satisfactory to the Agent, from the
Borrower and each Lender with respect to a new term sheet for the extension of
the revolving credit facilities (the date, if any, on which the Agent shall have
received such consent letters, the "Term Sheet Agreement Date"), the foregoing
extension shall automatically cease to be in effect and the reference to July
16, 2003 set forth herein shall automatically become a reference to June 24,
2003.

                  3. Representations and Warranties. The Borrower hereby
represents and warrants to the Agent and the Lenders that, as of the date hereof
and after giving effect to the amendment contained herein:

                  (a)      No Default or Event of Default has occurred and is
continuing.

                  (b)      The execution, delivery and performance by the
Borrower of this Amendment has been duly authorized by all necessary corporate
and other action and does not and will not require any registration with,
consent or approval of, notice to or action by, any person in order to be
effective and enforceable. Each of this Amendment and the Credit Agreement as
amended by this Amendment constitutes the legal, valid and binding obligation of
the Borrower, enforceable against each in accordance with its terms, subject to
applicable bankruptcy, insolvency, fraudulent conveyance, reorganization,
moratorium or other laws

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                                                                               2

affecting creditors' rights generally and subject to general principles of
equity, regardless of whether considered in a proceeding in equity or at law.

                  (c)      All representations and warranties of each Obligor
set forth in the Loan Documents as amended hereby are true and correct in all
material respects.

                  4. Covenants. The Borrower hereby agrees that during the
period commencing on the date hereof up to and including July 16, 2003 (the
"Extension Period"), the Borrower shall not take any action which could,
directly or indirectly, have a material adverse effect upon (i) the financial
condition, operations, assets (including power projects), business or prospects
of the Borrower and its Subsidiaries taken as a whole; or (ii) the ability of
the Borrower or any other Obligor to perform under any Loan Document. Without
prejudice to the foregoing, the Borrower shall ensure that, during the Extension
Period, (1) no Indebtedness is incurred, created, assumed or suffered to exist
by the Borrower or any of its Subsidiaries (except (A) Indebtedness under the
Loan Documents and the Loan Documents (as defined in the 2002 Credit Agreement),
(B) unsecured Indebtedness incurred in the ordinary course of business, other
than Indebtedness of the type described in (1) clauses (a), (c) or (f) of the
definition of "Indebtedness" and (2) clauses (b) and (g) of the definition of
"Indebtedness" with respect to any Indebtedness described in clause (1) above,
(C) other unsecured Indebtedness or Non-Recourse Debt (as defined in the Senior
Note Indentures) incurred in the ordinary course of business in connection with
Indebtedness existing or contractually committed to be made available as of the
date hereof, and (D) Indebtedness outstanding on the date hereof), and no
guarantee, collateral or other credit support is provided, and no Lien on the
properties of the Borrower or any of its Subsidiaries is created, incurred,
assumed or granted, in each case in support of (x) any Indebtedness (other than
Indebtedness permitted above) or (y) any obligation relating to any synthetic
lease transaction of the Borrower or any Subsidiary of the Borrower; (2) no
amendment, modification or supplement is made to any agreement or instrument
evidencing any Indebtedness, other than amendments, modifications or supplements
entered into in the ordinary course of business in respect of (A) the Credit
Agreement or the 2002 Credit Agreement, (B) any agreement or instrument
evidencing Non-Recourse Debt (as defined in the Senior Note Indentures) of a
Subsidiary of the Borrower, or (C) any agreement or instrument evidencing
Indebtedness other than Indebtedness of the type described in (1) clauses (a),
(c) or (f) of the definition of "Indebtedness" and (2) clauses (b) and (g) of
the definition of "Indebtedness" with respect to any Indebtedness described in
clause (1) above (the Indebtedness described in clauses (B) and (C) being
collectively referred to as "Excluded Indebtedness"); (3) no optional prepayment
is made on, or purchase or optional redemption is executed of, any Indebtedness
other than Excluded Indebtedness (including, without limitation, any buy-back or
defeasance of any outstanding bonds, puttable convertible bonds or other
securities of the Borrower or any of its Subsidiaries), it being understood and
agreed that, during the Extension Period, neither the Borrower or any of its
Subsidiaries shall obtain or receive any such Indebtedness (or instruments
evidencing same) in consideration of the sale or other transfer of any assets or
properties thereof; provided, that notwithstanding anything to the contrary
contained herein or in the Credit Agreement, at any time after the Term Sheet
Agreement Date, the Borrower shall be permitted to repurchase notes issued by
Calpine Canada Energy Finance II, ULC for an aggregate purchase amount not to
exceed US$50,000,000; (4) no Investment is made by the Borrower or any of its
Subsidiaries in any other Person (except (A) Investments by the Borrower in the
ordinary course of business in Subsidiaries the equity in which has been pledged
to the Lenders, and each of their respective Subsidiaries, (B)

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                                                                               3

Investments by the Borrower in other Persons pursuant to contractual commitments
existing as of the date hereof, and (C) Investments by the Borrower in CES in
support of transactions entered into by CES in the ordinary course of CES's
business, consistent with historical practices); and (5) all transactions
between any one or more of the Borrower and its Affiliates entered into during
the Extension Period are on terms that are fair and reasonable and similar to
those found in a comparable arm's length transaction with a Person that is not
an Affiliate of the Borrower. Notwithstanding the foregoing, it is agreed that
(x) the Borrower and its Subsidiaries may effectuate the transactions referred
to in Schedule I attached to the letter from the Borrower to the Lenders dated
May 20, 2003 and (y) none of the prohibitions contained in this Section 4 shall
be applicable insofar as they would otherwise constitute an encumbrance or
restriction in violation of Section 3.5 of the Pre-2000 Indentures (as defined
in the 2002 Credit Agreement). The provisions of this Section 4 may be amended,
modified or waived, if such amendment, modification or waiver is in writing and
consented to by the Borrower and Lenders owed or holding at least 51% of the
aggregate Revolving Loan Commitments and Commitments under the 2002 Credit
Agreement and the Credit Agreement, respectively (it being understood, however,
that no such amendment, modification or waiver shall amend, modify or waive the
provisions of the Credit Agreement unless such amendment, modification or waiver
satisfies the requirements of Section 11.1 of the Credit Agreement).

                  5. Conditions Precedent to Effectiveness. This Amendment shall
become effective as of the date hereof upon (i) the Agent having received
counterparts hereof duly executed and delivered by the Borrower and each Lender
and (ii) the Third Amendment, dated as of the date hereof, to the 2002 Credit
Agreement becoming effective in accordance with its terms.

                  6. No Other Amendments. Except as expressly amended hereby,
the provisions of the Credit Agreement are and shall remain in full force and
effect.

                  7. Expenses. The Borrower agrees to pay or reimburse the Agent
for its out-of-pocket expenses in connection with this Amendment, including the
reasonable fees, charges and disbursements of counsel to the Agent.

                  8. Governing Law; Counterparts. (a) This Amendment and the
rights and obligations of the parties hereto shall be governed by, and construed
and interpreted in accordance with, the laws of the State of New York.

                  (b)      This Amendment may be executed by one or more of the
parties to this Amendment on any number of separate counterparts, and all of
said counterparts taken together shall be deemed to constitute one and the same
instrument. This Amendment may be delivered by facsimile transmission of the
relevant signature pages hereof.

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                  IN WITNESS WHEREOF, the Borrower and the Lenders have caused
this Amendment to be duly executed by their respective authorized officers as of
the day and year first above written.

                                    CALPINE CORPORATION

                                    By   /s/ ROBERT D. KELLY
                                       -----------------------------------------
                                       Name: Robert D. Kelly
                                       Title: Chief Financial Officer

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                                    THE BANK OF NOVA SCOTIA, as Agent and Lender

                                    By   /s/ DENIS P. O'MEARA
                                       -----------------------------------------
                                       Name: Denis P. O'Meara
                                       Title: Managing Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    BANK OF AMERICA, NA

                                    By   /s/ THOMAS BIAGGI
                                       -----------------------------------------
                                       Name: Thomas Biaggi
                                       Title: Managing Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    BAYERISCHE LANDESBANK
                                    Cayman Islands Branch

                                    By   /s/ DIETMAR RIEG
                                       -----------------------------------------
                                       Name: Dietmar Rieg
                                       Title: First Vice President

                                    By   /s/ JAMES H. BOYLE
                                       -----------------------------------------
                                       Name: James H. Boyle
                                       Title: Vice President

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    CIBC INC.

                                    By   /s/ M. SANJEEVA SENANAYAKE
                                       -----------------------------------------
                                       Name: M. Sanjeeva Senanayake
                                       Title: Executive Director
                                           CIBC World Markets Corp. As Agent

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    CREDIT LYONNAIS NEW YORK BRANCH

                                    By   /s/ MARTIN C. LIVINGSTON
                                       -----------------------------------------
                                       Name: Martin C. Livingston
                                       Title: Vice President

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    CREDIT SUISSE FIRST BOSTON

                                    By   /s/ JAMES P. MORAN
                                       -----------------------------------------
                                       Name: James P. Moran
                                       Title: Director

                                    By   /s/ JAY CHALL
                                       -----------------------------------------
                                       Name: Jay Chall
                                       Title: Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    DRESDNER BANK AG, NEW YORK
                                    and GRAND CAYMAN BRANCHES

                                    By   /s/ FRED THURSTON
                                       -----------------------------------------
                                       Name: Fred Thurston
                                       Title: Vice President

                                    By   /s/ THOMAS R. BRADY
                                       -----------------------------------------
                                       Name: Thomas R. Brady
                                       Title: Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    FLEET NATIONAL BANK

                                    By   /s/ ANTHONY D. HEALEY
                                       -----------------------------------------
                                       Name: Anthony D. Healey
                                       Title: Authorized Signer

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    FORTIS CAPITAL CORP.

                                    By   /s/ HENDRIK VROEGO
                                       -----------------------------------------
                                       Name: Hendrik Vroego
                                       Title: Managing Director

                                    By   /s/ JIM TROUSDALE
                                       -----------------------------------------
                                       Name: Jim Trousdale
                                       Title: Assistant Vice President

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    BAYERISCHE HYPO-UND
                                    VEREINSBSBANK, AG NY BRANCH

                                    By   /s/ ANDREW G. MATHEWS
                                       -----------------------------------------
                                       Name: Andrew G. Mathews
                                       Title: Managing Director

                                    By   /s/ PAUL J. COLATRELLA
                                       -----------------------------------------
                                       Name: Paul J. Colatrella
                                       Title: Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    ING CAPITAL LLC

                                    By   /s/ STEPHEN E. FISCHER
                                       -----------------------------------------
                                       Name: Stephen E. Fischer
                                       Title: Managing Director

                                    By   /s/ G.D. BELLAMY, JR.
                                       --------------------------------
                                       Name: G.D. Bellamy, Jr.
                                       Title: Director

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    THE TORONTO DOMINION (TEXAS) INC.

                                    By   /s/ LYNN CHASIN
                                       -----------------------------------------
                                       Name: Lynn Chasin
                                       Title: Vice President

<PAGE>

                                    Signature page to the Seventh Amendment,
                                    dated as of June 16, 2003, to the Second
                                    Amended and Restated Credit Agreement, dated
                                    as of May 23, 2000, as amended, among
                                    Calpine Corporation, the various financial
                                    institutions as are or may become parties
                                    thereto and The Bank of Nova Scotia, as
                                    administrative agent.

                                    UNION BANK OF CALIFORNIA, N.A.

                                    By   /s/ BRYAN READ
                                       -----------------------------------------
                                       Name: Bryan Read
                                       Title: Vice President