Method for fabricating semiconductor device including self aligned gate

An method for fabricating a semiconductor device reduces a size of a MOSFET by self aligning a gate electrode with a device isolation insulation film. Thus, the gate electrode is not overlapped with the device isolation insulation film, differently from a conventional method for forming a MOSFET by partially overlapping the gate electrode with the device isolation insulation film in consideration of misalignment and CD variations in a mask process. As a result, a size of the MOSFET is reduced, thereby efficiently achieving the high integration of the semiconductor device.