Provided is a semiconductor device including an active region defined by a separation region on a main surface of a semiconductor substrate, and a field effect transistor formed in the active region. A boundary portion, over which a gate electrode pattern strides, is disposed in a boundary between the active region and the separation region and is configured such that a length of one side, in a direction of a gate length of the field effect transistor formed in the active region, becomes larger than the gate length and does not come into contact with at least one of a pair of source and drain regions of the field effect transistor.