The present invention provides a semiconductor device comprising a semiconductor element, a single-layer wiring board on which the semiconductor element is mounted, a connector section located at an end of the single-layer wiring board, a thermally and electrically conductive radiator plate, a relay electrode section formed on the single-layer wiring board, and a connecting member that electrically connects the radiator plate and the relay electrode section together. The single-layer wiring board is structured so that a power supply potential and/or a ground potential received by the connector section is transmitted through a path comprising the radiator plate, the relay electrode section, and the connecting member to the semiconductor element.