Abstract: This invention relates to a thin film semiconductor device and a method for fabricating it, and more particularly a thin film semiconductor device suitably applicable to a display device in an active matrix system and a method for fabricating it. In this invention, the structure of a thin film semiconductor device for improving the characteristic thereof and particularly the structure relative to the dominant orientation of a poly-Si film as an active layer of a thin film transistor (TFT) is disclosed. A method for fabricating a thin film semiconductor device which is capable of forming a poly-Si film at a relatively low process temperature is disclosed. Further, a display device in an active matrix system which provided high performance and high image quality is disclosed. The poly-Si film having a dominant orientation of (111) is formed by forming a poly-Si film on the semiconductor substrate at a temperature up to 570.degree. C. and annealing the substrate at a temperature up to 640.degree. C.