Effects of excess Si on the properities of the oxide of CVD tungsten silicide were investigated by comparing the characteristics of the two kinds of thermal oxide for CVD-WSi2.7 and WSi3.1 films on the polycrystalline Si film each other. It is reveraled from AES analysis that Si in the surface region of the silicide film is consumed to make composition and resistivity of the silicide film very nonuniform for the case of the oxidation of WSi3.1, while the underlayer polycrystalline Si was consumed for the case of the oxidation of WSi2.7.