A semiconductor device includes: a semiconductor substrate in which a SiGe layer having a first width in a channel direction is embedded in a channel forming region; gate insulating film formed on the channel forming region; a gate electrode formed on the gate insulating film and having a region protruding from a forming region of the SiGe layer with a second width wider than the first width; and source/drain regions having extension regions formed on the semiconductor substrate which sandwiches the channel forming region, thereby forming a field effect transistor, wherein the extension region is apart from the SiGe layer so that a depletion layer extending from a junction surface between the extension region and the semiconductor substrate does not reach the SiGe layer.