A semiconductor device that uses a high reliability TFT structure is provided. The gate electrode of an n-channel type TFT is formed by a first gate electrode and a second gate electrode that covers the first gate electrode. LDD regions have portions that overlap the second gate electrode through a gate insulating film, and portions that do not overlap. As a result, the TFT can be prevented from degradation in an ON state, and it is possible to reduce the leak current in an OFF state.