The present invention relates to a process for preparing a polycrystalline silicon thin film comprising a step of microwave annealing and crystallization of an amorphous thin film of silicon semiconductor, silicon semiconductor added with impurities, IV family semiconductor comprising Si alloy such as Si.sub.1 -.sub.x Ge.sub.x, III-V family and II-VI family semiconductor. The process for preparing polycrystalline silicon thin film of the present invention comprises the steps of: immersing a washed substrate into a deposition equipment and heating the substrate; depositing an amorphous or microcrystalline silicon thin film on the substrate; and, annealing the deposited thin film employing microwave for crystallization.