A lateral semiconductor device including a semiconductor substrate; a buried oxide layer formed on the semiconductor substrate, and an active layer formed on the buried oxide layer. The active layer includes a first conductivity type well region, a second conductivity type well region, and a first conductivity type drift region interposed between the first conductivity type well region and the second conductivity type well region. A region where current flows because of carriers moving between the first conductivity type well region and the second conductivity type well region, and a region where no current flows are formed alternately between the first conductivity type well region and the second conductivity type well region, in a direction perpendicular to a carrier moving direction when viewed in a plan view.