OFF current of a TFT is reduced. There is provided a semiconductor device includung: a substrate; a shielding film formed so as to be in contact with the substrate; a planarization insulating film formed on the substrate so as to cover the shielding film; and a semiconductor layer formed so as to be in contact with the planarization insulating film. The semiconductor device is characterized in that the shielding film overlaps the semiconductor layer with the planarization insulating film sandwiched therebetween, and that the planarization insulating film is polished by CMP before the semiconductor layer is formed.