Abstract: A horizontal semiconductor device includes an electrically conductive substrate having a first surface, a buffer layer disposed on the first surface of the substrate, an epitaxial unit disposed on the buffer layer opposite to the substrate, a first electrode unit disposed on the epitaxial unit, and a second electrode unit. The substrate has an exposed region that is exposed from the buffer layer and the epitaxial unit. The second electrode unit includes a first conductive member disposed on the epitaxial unit and spaced apart from the first electrode unit, and a second conductive member extending from the first conductive member to the exposed region.