We report on the formation of nickel silicide in nickel‐implanted amorphous silicon thin films. We have found that during annealing, precipitates of NiSi2form in the interior of the film. This is in contrast with results for interfacial reactions between nickel films and silicon, where the first phases to appear are Ni2Si and NiSi on amorphous silicon, and Ni2Si on crystalline silicon. We suggest that these results reflect differences in surface energies and their effects on silicide nucleation.