An image display device capable of high-resolution and smooth moving image display, equipped with TFTs in an n-type (or p-type) semiconductor layer with a high on-off ratio and a low resistance. In polysilicon crystallization by laser annealing, an n-type (or p-type) semiconductor layer with a low resistance is produced by performing the following processes in order: implanting nitrogen (N) ions into an amorphous silicon precursor semiconductor film; laser crystallization; implanting n-type (or p-type) dopant ions; and annealing for dopant activation. When fabricating TFTs, this low-resistance semiconductor layer is used to form a source and a drain. Since C, N, and O impurities decrease the mobility of the TFTs, polysilicon is used in which the contaminants concentrations meet the following conditions: carbon concentration ≦3×1019 cm−3, nitrogen concentration ≦5×1017 cm−3, and oxygen concentration ≦3×1019 cm−3.