Formation of vanadium silicides by the interactions of vanadium with bare and oxidized Si wafers has been studied by both x-ray diffraction and He ion backscattering techniques. X-ray diffraction was used to identify phases and ion backscattering to profile compositional changes. In the case of V on Si, the silicide VSi2, which is a silicon-rich phase, was found to form at temperatures from 600 to 1000°C. In the case of V on SiO2, reactions took place only at temperatures above 800°C, and the reaction products were identified to be V3Si, V5SI3, and V2O5. Both V3Si and V5Si 3 are vandium-rich phases, and the V3Si that we found was a continuous layer between the substrate and the other two phases, and became superconducting at about 15°K.