Semiconductor device and manufacturing method thereof

A method of manufacturing a semiconductor device having a field effect transistor with improved current driving performance (increase of drain current) of a field effect transistor comprising the steps of ion implanting a group IV element from the main surface to the inside of a silicon layer as a semiconductor substrate to a level shallower than the implantation depth of the impurities in the step of forming the semiconductor region before the step of ion implanting impurities from the main surface to the inside of the silicon layer as a semiconductor substrate to form the semiconductor region being aligned with the gate electrode.