Crystallization of amorphised thin silicon layer on insulator (SOI), and subsequently doped by As implantation has been investigated after furnace annealing at 680 °C or laser irradiation in the milliseconds regime. In partly crystallized intrinsic amorphous SOI grains are 3 times larger than the ones observed in implanted layers produced by chemical vapor deposition. In the As implanted SOI, the density of grains is reduced whilst their size increases up to a factor 8 at 3×1015 As/cm2. The presence of As increases both the nucleation barrier and the grain growth velocity. Similar effects were observed after laser annealing.