An object of the present invention is to provide a method for easily forming a polycrystalline semiconductor thin-film, such as polycrystalline silicon having high crystallinity and high quality, or a single crystalline semiconductor thin-film at inexpensive cost, the crystalline semiconductor thin-film having a large area, and to provide an apparatus for processing the method described above. In forming a polycrystalline (or single crystalline) semiconductor thin-film (7), such as a polycrystalline silicon thin-film, having high crystallinity and a large grain size on a substrate (1), or in forming a semiconductor device having the polycrystalline (or single crystalline) semiconductor thin-film (7) on the substrate (1), a method comprises forming a low-crystallization semiconductor thin-film (7A) on the substrate (1), and subsequently heating and cooling this low-crystallization semiconductor thin-film (7A) to a fusion, a semi-fusion, or a non-fusion state by flash lamp annealing to facilitate the crystallization of the low-crystallization semiconductor thin-film, whereby a polycrystalline (single crystalline) semiconductor thin-film (7) is obtained. A method for forming the semiconductor device and an apparatus for processing the methods are also disclosed.