When a Si crystal substrate is covered with evaporated Au and heated at relatively low temperatures (100–300 °C) in an oxidizing atmosphere, because of the Si&sngbnd;Au reaction at the interface, a SiO2layer is readily formed over the Au layer. Present Auger spectroscopic study concludes that the reaction induces a Si&sngbnd;Au mixed phase that is almost identical with the Si&sngbnd;Au alloyed phase obtained by heat treatment in a high vacuum at temperatures well above the Si&sngbnd;Au eutectic point (370 °C). The Auger spectra of Si in both the mixed and alloyed phases differ obviously from that of the pure Si crystal.