<PAGE>

                                                                    EXHIBIT 10.8


Certificate Number C-1                                    310 Common Securities

         THIS COMMON SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT
OF 1933, AS AMENDED, AND MAY NOT BE OFFERED, SOLD, PLEDGED OR OTHERWISE
TRANSFERRED EXCEPT PURSUANT TO AN EXEMPTION FROM REGISTRATION.

         THIS CERTIFICATE IS NOT TRANSFERABLE EXCEPT IN COMPLIANCE WITH SECTION
8.1 OF THE DECLARATION.

                               September 26, 2002

             Certificate Evidencing Floating Rate Common Securities

                                       of

                         AmericanWest Statutory Trust I

         AmericanWest Statutory Trust I, a statutory trust created under the
laws of the State of Connecticut (the "Trust"), hereby certifies that
AmericanWest Bancorporation (the "Holder") is the registered owner of common
securities of the Trust representing undivided beneficial interests in the
assets of the Trust (the "Common Securities"). The designation, rights,
privileges, restrictions, preferences and other terms and provisions of the
Common Securities represented hereby are issued pursuant to, and shall in all
respects be subject to, the provisions of the Amended and Restated Declaration
of Trust of the Trust dated as of September 26, 2002, among Wesley E. Colley,
Wade Griffith and John L. Gilbert, as Administrators, State Street Bank and
Trust Company of Connecticut, National Association, as Institutional Trustee,
AmericanWest Bancorporation, as Sponsor, and the holders from time to time of
undivided beneficial interest in the assets of the Trust including the
designation of the terms of the Common Securities as set forth in Annex I to
such amended and restated declaration, as the same may be amended from time to
time (the "Declaration"). Capitalized terms used herein but not defined shall
have the meaning given them in the Declaration. The Holder is entitled to the
benefits of the Guarantee to the extent provided therein. The Sponsor will
provide a copy of the Declaration, the Guarantee and the Indenture to the Holder
without charge upon written request to the Sponsor at its principal place of
business.

         As set forth in the Declaration, where an Event of Default has occurred
and is continuing, the rights of Holders of Common Securities to payment in
respect of Distributions and payments upon Liquidation, redemption or otherwise
are subordinated to the rights of payment of Holders of the Capital Securities.

         Upon receipt of this Certificate, the Holder is bound by the
Declaration and is entitled to the benefits thereunder.

         By acceptance of this Certificate, the Holder agrees to treat, for
United States federal income tax purposes, the Debentures as indebtedness and
the Common Securities as evidence of undivided beneficial ownership in the
Debentures.

         This Common Security is governed by, and construed in accordance with,
the laws of the State of Connecticut, without regard to principles of conflict
of laws.

                     Signature appears on the following page

<PAGE>

         IN WITNESS WHEREOF, the Trust has duly executed this certificate.

                                        AMERICANWEST STATUTORY TRUST I


                                        By:_____________________________________
                                           Name:
                                           Title: Administrator

<PAGE>

                           REVERSE OF COMMON SECURITY

         Distributions payable on each Common Security will be identical in
amount to the Distributions payable on each Capital Security, which is at an
annual rate equal to 5.220% beginning on (and including) the date of original
issuance and ending on (but excluding) December 26, 2002 and at an annual rate
for each successive period beginning on (and including) December 26, 2002, and
each succeeding Distribution Payment Date, and ending on (but excluding) the
next succeeding Distribution Payment Date (each a "Distribution Period"), equal
to 3-Month LIBOR, determined as described below, plus 3.400% (the "Coupon
Rate"); provided, however, that prior to September 26, 2007, the Coupon Rate
shall not exceed 11.90%, applied to the stated liquidation amount of $1,000.00
per Common Security, such rate being the rate of interest payable on the
Debentures to be held by the Institutional Trustee. Distributions in arrears for
more than one quarterly period will bear interest thereon compounded at the
Distribution Rate (to the extent permitted by applicable law). The term
"Distributions" as used herein includes payments of Interest and any principal
on the Debentures held by the Institutional Trustee unless otherwise stated. A
Distribution is payable only to the extent that payments are made in respect of
the Debentures held by the Institutional Trustee and to the extent the
Institutional Trustee has funds available therefor. As used herein,
"Determination Date" means the date that is two London Banking Days (i.e., a
business day in which dealings in deposits in U.S. dollars are transacted in the
London interbank market) preceding the commencement of the relevant Distribution
Period. In the event that any date on which a Distribution is payable on this
Common Security is not a Business Day, then a payment of the Distribution
payable on such date will be made on the next succeeding day which is a Business
Day (and without any Distribution or other payment in respect of any such
delay), except that, if such Business Day is in the next succeeding calendar
year, such payment shall be made on the immediately preceding Business Day, in
each case with the same force and effect as if made on the date the payment was
originally payable. The amount of interest payable for the Distribution Period
commencing December 26, 2002 and each succeeding Distribution Period will be
calculated by applying the Coupon Rate to the principal amount outstanding at
the commencement of the Distribution Period and multiplying each such amount by
the actual number of days in the Distribution Period concerned divided by 360.

         "3-Month LIBOR" as used herein, means the London interbank offered
interest rate for three-month U.S. dollar deposits determined by the Debenture
Trustee in the following order of priority: (i) the rate (expressed as a
percentage per annum) for U.S. dollar deposits having a three-month maturity
that appears on Telerate Page 3750 as of 11:00 a.m. (London time) on the related
Determination Date ("Telerate Page 3750" means the display designated as "Page
3750" on the Dow Jones Telerate Service or such other page as may replace Page
3750 on that service or such other service or services as may be nominated by
the British Bankers' Association as the information vendor for the purpose of
displaying London interbank offered rates for U.S. dollar deposits); (ii) if
such rate cannot be identified on the related Determination Date, the Debenture
Trustee will request the principal London offices of four leading banks in the
London interbank market to provide such banks' offered quotations (expressed as
percentages per annum) to prime banks in the London interbank market for U.S.
dollar deposits having a three-month maturity as of 11:00 a.m. (London time) on
such Determination Date. If at least two quotations are provided, 3-Month LIBOR
will be the arithmetic mean of such quotations; (iii) if fewer than two such
quotations are provided as requested in clause (ii) above, the Debenture Trustee
will request four major New York City banks to provide such banks' offered
quotations (expressed as percentages per annum) to leading European banks for
loans in U.S. dollars as of 11:00 a.m. (London time) on such Determination Date.
If at least two such quotations are provided, 3-Month LIBOR will be the
arithmetic mean of such quotations; and (iv) if fewer than two such quotations
are provided as requested in clause (iii) above, 3-Month LIBOR will be a 3-Month
LIBOR determined with respect to the Distribution Period immediately preceding
such current Distribution Period. If the rate for U.S. dollar deposits having a
three-month maturity that initially appears on Telerate Page 3750 as of 11:00
a.m. (London time) on the related Determination Date is superseded on the
Telerate Page 3750 by a corrected rate by 12:00 noon (London time) on such
Determination Date, then the corrected rate as so substituted on the applicable
page will be the applicable 3-Month LIBOR for such Determination Date.

         The Coupon Rate for any Distribution Period will at no time be higher
than the maximum rate then permitted by New York law as the same may be modified
by United States law.

         All percentages resulting from any calculations on the Common
Securities will be rounded, if necessary, to the nearest one hundred-thousandth
of a percentage point, with five one-millionths of a percentage point rounded
upward (e.g., 9.876545% or .09876545 being rounded to 9.87655% or .0987655, and
all dollar amounts used in or resulting from such calculation will be rounded to
the nearest cent (with one-half cent being rounded upward)).

         Except as otherwise described below, Distributions on the Common
Securities will be cumulative, will accrue from the date of original issuance
and will be payable quarterly in arrears on March 26, June 26, September 26 and
December 26 of each year, commencing on December 26, 2002. The Debenture Issuer
has the right under the Indenture to defer payments of interest on the
Debentures by extending the interest payment period for up to 20 consecutive
quarterly periods (each an "Extension Period") on the Debentures, subject to the
conditions described below, although such interest would continue to accrue on
the Debentures at an annual rate equal to the Distribution Rate compounded
quarterly to the extent permitted by law during any Extension Period. No
Extension Period may end on a date other than an Interest Payment Date. At the
end of any such Extension Period the Sponsor shall pay all interest then accrued
and unpaid on the Debentures (together with Additional Interest thereon);
provided, however, that no Extension Period may extend beyond the Maturity Date.
Prior to the termination of any Extension Period, the Sponsor may further extend
such period, provided that such period together with all such previous and
further consecutive extensions thereof shall not exceed 20 consecutive quarterly
periods, or extend beyond the Maturity Date. Upon the termination of any
Extension Period and upon the payment of all accrued and unpaid interest and
Additional Interest, the Sponsor may commence a new Extension Period, subject to
the foregoing requirements. No interest or Additional Interest shall be due and
payable during an Extension Period, except at the end thereof, but each
installment of interest that would otherwise have been due and payable during
such Extension Period shall bear Additional Interest. If Distributions are
deferred, the Distributions due shall be paid on the date that the related
Extension Period terminates, to Holders of the Securities as they appear on the
books and records of the Trust on the record date immediately preceding such
date. Distributions on the Securities must be paid on the dates payable (after
giving effect to any Extension Period) to the extent that the Trust has funds
available for the payment of such distributions in the Property Account of the
Trust. The Trust's funds available for Distribution to the Holders of the
Securities will be limited to payments received from the Debenture Issuer. The
payment of Distributions out of moneys held by the Trust is guaranteed by the
Guarantor pursuant to the Guarantee.

         The Common Securities shall be redeemable as provided in the
Declaration.

<PAGE>

                                   ASSIGNMENT

      FOR VALUE RECEIVED, the undersigned assigns and transfers this Common
Security Certificate to:

      __________________________________________________________________________


      (Insert assignee's social security or tax identification number)__________

      __________________________________________________________________________

      __________________________________________________________________________


      (Insert address and zip code of assignee) and irrevocably appoints

      __________________________________________________________________________


                   ________________________________________________  agent    to
                   transfer this Common Security Certificate on the books of the
                   Trust. The agent may substitute another to act for him or
                   her.

                   Date:_________________________________________

                   Signature:______________________________

                   (Sign exactly as your name appears on the other side of this
                   Common Security Certificate)

                   Signature:______________________________

                   (Sign exactly as your name appears on the other side of this
                   common Security Certificate)

         Signature Guarantee/1/



________________________________
         /1/ Signature must be guaranteed by an "eligible guarantor institution"
         that is a bank, stockbroker, savings and loan association or credit
         union, meeting the requirements of the Security registrar, which
         requirements include membership or participation in the Securities
         Transfer Agents Medallion Program ("STAMP") or such other "signature
         guarantee program" as may be determined by the Security registrar in
         addition to, or in substitution for, STAMP, all in accordance with the
         Securities Exchange Act of 1934, as amended.