An insulated gate transistor is comprised of a semiconductor thin film, a first gate insulating film formed on a main surface of the semiconductor thin film, a first conductive gate formed on the first gate insulating film, first and second confronting semiconductor regions of a first conductivity type insulated from the first conductive gate and disposed in contact with the semiconductor thin film, and a third semiconductor region of a second conductivity type opposite to the first conductivity type and disposed in contact with the semiconductor thin film. The insulated gate transistor is controlled by injecting carriers of the second conductivity type into the semiconductor thin film from the third semiconductor region, and thereafter applying a first electric potential to the first conductive gate to form a channel of the first conductivity type on a portion of the semiconductor thin film disposed between the first semiconductor region and the second semiconductor region.