Small angle x‐ray scattering measurements were performed on arsenic‐implanted laser‐annealed silicon slices to investigate the features of precipitation at 900°C for different dopant supersaturations. With decreasing As concentration from , the size distribution of the precipitates shifts toward larger values and their shape evolves from that of thin platelets, becoming three‐dimensional and approaching at last that of a sphere. The high concentration diffusivity of As at 900°C, deduced from the size of the largest precipitates in specimens doped , turns out to be . Determinations of the shift of the carrier concentration profiles and of the junction depth, after heating at 1000°C, show that the diffusivity of As is not affected by the precipitation and, hence, is controlled by the concentration of the dopant.