We investigated the effect of infrared continous wave laser irradiation on amorphous silicon layers deposited by plasma enhanced chemical vapor deposition. Crystallization occurs via spontaneous nucleation at high temperature or by layer melting and solidification. Amorphous layers of thickness in the range 50– 1000 nm 50–1000nm have been crystallized up to 80% of their volume. We observed a two-dimensional growth when the thickness is 50 nm 50nm, whereas a three-dimensional growth occurs for thicker layers with an average grain size of< 30 nm< 30nm, weakly dependent on the thickness. We also found that hydrogen desorption occurs without layer degradation, regardless of the layer thickness. The coalescence of hydrogen before outdiffusion produces voids only for layers thicker than 200 nm 200nm, whose presence reduces the average grain size by a factor of 2–3.