We studied the sidewall oxidation behavior of dichlorosilane-based WSix/P-doped Si stack gate electrode and compared to that of monosilane-based WSix . WSix was known to be abnormally oxidized during reoxidation after gate stack patterning, resulting in deformation of the sidewall profile of gate electrode. We found that low temperature oxide for mask of gate patterning was effective to prevent the abnormal oxidation, Preannealing at temperature higher than 800 degreesC was also found to effectively suppress the abnormal oxidation of crystalline WSix.