Formation of Co germanosilicides on Si 0.8 Ge 0.2 virtual substrates with a Co/Au/Co sandwich thin film after different heat treatments has been investigated. The sequence of phase formation is the same as the reaction of blanket Co thin film with (001)Si. The presence of thin interposing Au layers was found to significantly enhance the formation of low-resistivity CoSi 2 on (001)Si 0.8 Ge 0.2 substrates. The formation temperature of CoSi 2 phase in the Co/Au/Co/(001)Si 0.8 Ge 0.2 samples was lowered by about 200 °C compared to that of Co/(001)Si 0.8 Ge 0.2 samples. From TEM and EDS analysis, some of Au atoms were found to diffuse from the original interface position to disperse within the CoSi 2 layers during silicidation reactions. The mechanisms for the enhanced formation of CoSi 2 in the Co/Au/Co/Si 0.8 Ge 0.2 system were explained in the context of classical nucleation theory.