A laser annealing method for obtaining a crystalline semiconductor film having a large grain size is provided. Laser light is irradiated to the top surface and the bottom surface of an amorphous semiconductor film when crystallizing the amorphous semiconductor film by laser light irradiation. Furthermore, a relationship of 0<(I.sub.0'/I.sub.0)<1, or 1<(I.sub.0'/I.sub.0) is achieved for the ratio (I.sub.0/I.sub.0') between the effective energy strength of the laser light when irradiated to the top surface (I.sub.0) and the effective energy strength of the laser light when irradiated to the bottom surface (I.sub.0').