A switching device provided herewith includes first to fourth semiconductor layers and a gate electrode. The second semiconductor layer is of a first conductive type or an un-dope type and located on the first semiconductor layer. A hetero junction is formed between the first and the second semiconductor layers. The third semiconductor layer is of a second conductive type and located on the second semiconductor layer. The fourth semiconductor layer is of a second conductive type and located on the third semiconductor layer. A hetero junction is formed between the third and the fourth semiconductor layers. The gate electrode electrically connected to the fourth semiconductor layer.