October 18, 2005 – MEMC Electronic Materials Inc., St. Peters, MO, has received a favorable ruling from the Opposition Division of the European Patent Office regarding the manufacture and use of semiconductor-grade, single-crystal, defect-free silicon wafers having a diameter of 200mm or greater. This type of defect-free silicon wafer, trademarked by MEMC as Perfect Silicon, enables semiconductor manufacturers to produce next-generation devices with enhanced performance characteristics. The patent was first filed in 1998, granted in 2001, and opposed by Sumitomo Mitsubishi Silicon Corp. (SUMCO), a manufacturer of electronic-grade silicon wafers for the semiconductor industry, in 2002. MEMC also recently received a favorable appellate ruling in a patent infringement case against SUMCO in the US, which relates to the counterpart US patent. The US patent infringement case is expected to go to trial in 2006.