According to an aspect of the present invention, there is provided a semiconductor device including: a semiconductor substrate; active areas with island-like shapes formed on the semiconductor substrate; an element isolation area surrounding the active areas and including an element isolation groove formed on the semiconductor substrate and an element isolation film embedded into the element isolation groove; gate insulating films each formed on corresponding one of the active areas and having a first end portion that overhangs from the corresponding active area onto the element isolation area at one side and a second end portion that overhangs from the corresponding active area onto the element isolation area at the other side, wherein an overhang of the first end portion has a different length from a length of an overhang of the second end portion.