A semiconductor device according to a first aspect of the present invention includes a device main body, a single power supply wiring board, a plurality of output wiring boards, and a plurality of semiconductor elements. In a long-side direction of the device main body, the narrow portion of one of any two adjacent wiring boards faces the wide portion of another one of the any two adjacent wiring boards. In a short-side direction of the device main body, the narrow portion and the wide portion of each of the output wiring boards respectively face the wide portion and the narrow portion, in a single pair, of the power supply wiring board. In the long-side direction of the device main body a width of each of the output wiring boards is smaller than a sum of widths of the narrow portion and the wide portion, in a single pair, of the power supply wiring board.