Disclosed is a semiconductor device wherein the switching speed of a transistor is increased. Specifically disclosed is a semiconductor device comprising a semiconductor layer formed on a part of an insulating layer, a first transistor formed on a lateral face of the semiconductor layer and having a first gate insulating film, a first gate electrode and two first impurity layers forming a source and a drain, and a second transistor formed on another lateral face of the semiconductor layer and having a second gate insulating film, a second gate electrode and two second impurity layers forming a source and a drain.