Alloy films of NiPt were e-beam codeposited on n-type Si and annealed up to 700°C in a purified- He ambient furnace. Silicide formation was monitored using MeV4 He Rutherford backscattering and glancing-angle x-ray diffraction. At low temperatures (300-350°C), Ni segregates at the Si/ silicide interface and the first phases detected are NiSi and PtSi. At intermediate temperatures (400-500°C), there is further accumulation of Ni at the Si/silicide interface, and at later stages an incursion of Pt to the interface. The barrier height increase reflects the presence of Pt. At 700°C, the Ni and Pt redistribute to form a uniform ternary.