Interfacial reactions in Pt/InP contacts were examined by transmission electron microscopy and Auger depth profiling. A solid state amorphization reaction occurred after the contacts were annealed for 60 s at 325 °C. Crystallites were observed in the amorphous layer near the boundary between the amorphous phase and the remaining Pt upon annealing at 350 °C. The predominant phase formed upon crystallization was polycrystalline Pt5InP. A cubic phase, which is most likely a supersaturated solution of phosphorus in Pt3In, also formed. As the annealing temperature was increased, the reaction proceeded with the formation of phases that were richer in In and P. For 60 s anneals at temperatures of 500 °C or greater, Pt‐In phases and textured PtP2were observed, and the film/InP interface exhibited roughness on the scale of tens of nanometers. Both the Pt‐In phases and PtP2were present at the film/InP interface.