It was observed that thin metal (catalytic metal: platinum) penetrated into a interface between a chemical vapor deposition (CVD) silicon dioxide film and a Si–implanted electric thermal furnace, on the way to carrying out experiments on alloyed ohmic–metals with Si–implanted electrically conductive n–type GaAs crystal layers in order to obtain stable and uniform ohmic contact electrodes of low specific ohmic contact resistances for metal–semiconductor field–effect–transistor arrays as a observation tool of semi–insulating GaAs–crystal crystallographic uniformity.