In a crystallization process of an amorphous semiconductor film, a first polycrystalline semiconductor film, in which amorphous regions are dotted within the continuous crystal region, is obtained by performing heat treatment after introducing a metallic element which promotes crystallization on the amorphous semiconductor film. At this point, the amorphous regions are kept within a predetermined range. A laser beam having a wave length region, which can give more energy to the amorphous region than to the crystal region, is irradiated to the first polycrystalline semiconductor film, it is possible to crystallize the amorphous region without destroying the crystal region. If a TFT is manufactured based on a second polycrystalline semiconductor film, which is obtained through the above-mentioned crystallization processes, the TFT with high electric characteristics and less fluctuation can be obtained.