A semiconductor device having a silicon-on-insulator (SOI) structure in which a source region and a drain region extend along a longitudinal direction that is a direction along a longer side of sides facing each other, and are disposed side-by-side in a lateral direction that is a direction perpendicular to the longitudinal direction. In a plan view, a body region extends along the longitudinal direction and is surrounded by a drift region and an insulating region. A space between the insulating region and the body region in the lateral direction becomes narrower from the center to the end of the body region in the longitudinal direction. This achieves high breakdown voltage in the semiconductor device.