AMENDMENT NO. 1 TO SUPPLY AGREEMENT (SUNTECH CONTRACT NO. PUR1-0706092))

This Amendment No. 1 (this “Amendment”) is effective as of August 30, 2007, by
and between Hoku Materials, Inc., a Delaware corporation (“HOKU”), and Wuxi
Suntech Power Co., Ltd., a People’s Republic of China company (“SUNTECH”). HOKU
and SUNTECH are each a “Party” and together the “Parties” to this Amendment No.
1.

RECITALS

Whereas, HOKU and SUNTECH are Parties to that certain Supply Agreement (Suntech
Contract No. PUR1-0706092) dated as of June 13, 2007 (the “Supply Agreement”)
Whereas, the Parties desire to make certain amendments to the Supply Agreement
as hereinafter set forth Whereas, each Party derives a benefit from the
amendments set forth herein, Now therefore, in consideration of the foregoing,
and for other good and valuable consideration, the receipt of which is hereby
acknowledged by the Parties, the Parties agree to amend the Supply Agreement as
set forth below.

AGREEMENT

1. Definitions. All capitalized terms not otherwise defined are defined in the
Supply Agreement.

2. Amendment of Section 5.3.3 of the Supply Agreement. The Parties agree that
all references to “Bank of China” are removed from Section 5.3.3 of the Supply
Agreement.

3. Amendment of Section 11.5 of the Supply Agreement. Section 11.5 of the Supply
Agreement is hereby amended and restated in its entirety to read as follows:

11.5 HOKU has not entered into any additional supply contract with, or made any
supply commitment to, any third party (not including the long term supply
contract that HOKU and SANYO entered into prior to the Effective Date) where the
aggregate of HOKU’s delivery obligations under all of its supply contracts
(including those with SUNTECH and SANYO) and such additional supply
contract/commitment during any month exceeds the rated monthly production
capacity of all Reactors as certified by the manufacturer thereof, except for
(A) supply contracts for additional capacity from Facility expansion, including
pre-sales of potential Facility expansions, or from increased productivity of
the Reactors, and (B) sales on the spot market or long-term contracts for the
sale of polysilicon that does not meet the Product Specifications, provided that
HOKU has used commercially reasonable efforts to meet the Product Specifications
with respect to such polysilicon and that HOKU is not manufacturing polysilicon
for the purpose of making such spot market sales or fulfilling such long term
contracts.

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IN WITNESS WHEREOF, the Parties have executed this Supply Agreement as of the
date first set forth above.

SUNTECH:    HOKU:      WUXI SUNTECH POWER CO., LTD.    HOKU MATERIALS, INC. 
By:    /s/ Steven Chan    By:     /s/ Dustin Shindo  Name:    Steven Chan   
Name:     Dustin Shindo  Title:    VP, Business Development    Title:   
Chairman & CEO  Authorized Signatory    Authorized Signatory 

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