In a fabrication process of a semiconductor device for use in a TFT liquid crystal display system, before the start of crystallizing amorphous silicon (a-Si), dehydrogenation annealing is carried out to not only decrease the density of hydrogen in the p-Si film (13) to 510²⁰ atoms/cm³ at most but also to prevent crystallization of the a-Si film (13) being obstructed due to possible excessive hydrogen remaining in the film. With the p-Si film (13) covered with an interlayer insulation film (15) in the form of a plasma nitride film, annealing is then carried out in nitrogen atmosphere at a temperature of 350 C. to 400 C. for one to three hours, more preferably 400 C. for two hours. The result is that hydrogen atoms in the p-Si film (13) efficiently terminate dangling bonds of the film and hence do not become excessive, thus improving the electrical characteristics of the semiconductor device.