China's Ministry of Commerce said on Monday that it will impose provisional anti-subsidy duties on some US exports of solar-grade polysilicon, a major material for making solar cells.

The ministry said a preliminary investigation found that some solar-grade polysilicon imports from the United States were subsidized, which had caused "substantial damage" to Chinese producers.

Starting from September 20, Chinese importers of the product from US companies, including Hemlock Semiconductor Corp. and AE Polysilicon Corp., will be required to pay a deposit rate of up to 6.5 percent, the ministry said in a statement.

It said other companies, including REC Solar Grade Silicon LLC, REC Advanced Silicon Materials LLC and MEMC Pasadena, Inc., would not be subject to the duties because they had not been subsidized or the rates were too low.

The announcement comes after the ministry slapped anti-dumping duties of 53.3 percent to 57 percent on US solar-grade polysilicon imports in July.