Silicon‐metal systems are highly susceptible to solid‐solid reactions which modify their electrical and mechanical properties. Although many works are dealing with silicide formation, the molybdenum‐silicon system has not yet been investigated in detail to our knowledge. In this paper we present a He+ion backscattering study of the molybdenum‐silicide formation by interaction of a thin molybdenum layer and a silicon ⟨111⟩ wafer. The silicide phases Mo3Si and MoSi2have been identified by x‐ray diffraction and transmission electron microscopy. Surface transformations were observed by scanning electron microscopy. For an 800‐A˚ Mo layer sputter deposited on silicon, we have found a time‐square growth rate for MoSi2with an average activation energy of 2.4 eV in the temperature range 475–550 °C. The fundamental roles of the cleaning of the silicon surface, of the substrate temperature during sputtering, and of the stresses in the layer are pointed out.