Dow Corning Corporation and its Hemlock Semiconductor Group  subsidiaries have applied to the Foreign-Trade Zones Board for subzone authority.  This is an effort to hold down the costs of supplying silicones and polysilicons that are manufactured in Michigan and sold to both foreign and domestic customers.  The U.S. supply of silicon metal only satisfies half the current American demand, and so substantial quantities are imported, with significant antidumping duties assessed on some of the sources.  The Foreign-Trade Zone designation would help offset some of these costs to support U.S. based manufacturing in the Midland plants.  "For U.S. companies to thrive in global markets, they must have access to raw materials at competitive global prices,"  said Daniel Griswold, President, National Association of Foreign-Trade Zones