The reaction rate of vacuum‐evaporated films of V of the order of 1000 Å thick is investigated by MeV He backscattering spectrometry. On substrates of single‐crystal Si and for anneal times up to several hours in the temperature range 570–650°C, VSi2is formed at a linear rate in time. The activation energy of the process is 1.7±0.2 eV. The presence of oxygen in amounts of 10% can significantly decelerate the reaction. On substrates of SiO2in the temperature range 730–820°C and anneal times of several hours or less, V3Si is formed at a square‐root rate in time. The activation energy of this process is 2.0±0.2 eV.