An object of the present invention is to provide a technique for improving characteristics of a TFT and realizing the structure of the TFT optimal for driving conditions of a pixel section and a driving circuit, using a smaller number of photo masks. A semiconductor device has a semiconductor film, a first electrode, and a first insulating film sandwiched between the semiconductor film and the first electrode, and further has a second electrode, and a second insulating film sandwiched between the semiconductor film and the second electrode. The first electrode and the second electrode overlap with each other across a channel-formed region which the semiconductor film has. A constant voltage is applied to the first electrode at any time.