PURPOSE: To obtain a polycrystalline silicon semiconductor film which has an excellent electric characteristic by a method wherein a hydrogenated amorphous silicon film is formed at low temperatures and is heat-treated in a vacuum and then it is dehydrogenated to generate a dangling bond in the film and the excimer laser is cast on the film in a vacuum-unbroken state.

CONSTITUTION: An SiO2 film or silicon nitride film is formed as a base protective film 12 on a glass substrate 11. Nextly, an intrinsic hydrogenated amorphous silicon semiconductor layer 13 is formed in the thickness of 100nm by the plasma CVD method. At that time, by setting the film formation temperature low, the formed amorphous silicon film is allowed to have in it a good quantity of water and bonds of silicon are neutralized with hydrogen as much as possible. Nextly, a device separation patterning is conducted and the sample is heated in a vacuum at 450°C for one hour to be dehydrogenated completely and dangling bonds (unpaired bonds) are generated in high density in the film. With the vacuum state being maintained, the excimer laser is cast on the sample to crystallize it.