A semiconductor device having a lateral semiconductor element includes a semiconductor substrate, a first electrode on the substrate, a second electrode on the substrate, and an isolation structure located in the substrate to divide the substrate into a first island and a second island electrically insulated from the first island. The lateral semiconductor element includes a main cell located in the first island and a sense cell located in the second island. The main cell causes a first current to flow between the first electrode and the second electrode so that the first current flows in a lateral direction along the surface of the substrate. The first current is detected by detecting a second current flowing though the sense cell.