The reaction of Ni- refractory metal alloys with silicon has been studied by backscattering spectrometry and transmission electron microscopy. The analysis of the as-deposited sample revealed solid solutions for Ni-Cr and amorphous phases for Ni-Ta and Ni-Ti. In situ annealing resulted in crystallization of Ni43 Ta57 at 750 °C, a value above the reaction temperature of the alloy with silicon. The amorphous alloy of Ni48Ti52 was transformed into the equilibrium compound of NiTi at 450 °C, much below the reaction temperature. Phase separation has been observed in the Ni-Cr and Ni-Ta systems with a Ni- silicide layer next to the Si substrate and a refractory disilicide layer on the other side. In contrast, Si reacts with the NiTi compound to form a uniform mixed layer with a composition of NiTiSi2. The different behavior is explained based on considerations of both thermodynamic and kinetic terms.