Interfacial reactions between Ti-Ta alloy films and single crystal Si have been studied by Auger electron spectroscopy, transmission electron microscopy and X-ray diffraction. It has been found that only binary compounds, silicides of each of the metals, and not any ternary compounds, are formed. The reaction products at the early stages of the reaction are Ta5Si3, TaSi2 and the metastable (C49 structure) TiSi2. The final stage of the reaction consists of a uniform intermixing of the disilicides, TiSi2 and TaSi2. Alloying causes a shift in the temperature of silicide formation to intermediate values between those for pure Ti and Ta (500 and 700°C, respectively), and this value increases with Ta content in the alloy film.