A semiconductor device (100, 300) comprising: a substrate (12, 52) that is annular or partially annular, the substrate (12, 52) having an inner circumferential portion arcuate in plan view and an outer circumferential portion arcuate in plan view; a first phase control circuit on the substrate (12, 52), the first phase control circuit being configured to control a first phase of a plurality of phases of a motor; a second phase control circuit on the substrate (12, 52) so as to be adjacent to the first phase control circuit in a circumferential direction of the substrate (12, 52), the second phase control circuit being configured to control a second phase of the plurality of phases of the motor, the second phase being different from the first phase; a power supply wiring on one of an outer circumferential side and an inner circumferential side of the first phase control circuit and the second phase control circuit in a radial direction of the substrate (12, 52), the power supply wiring being connected to the first phase control circuit and the second phase control circuit, and the power supply wiring extending in the circumferential direction of the substrate (12, 52); and a ground wiring on another one of the outer circumferential side and the inner circumferential side of the first phase control circuit and the second phase control circuit in the radial direction of the substrate (12, 52), the ground wiring being connected to the first phase control circuit and the second phase control circuit, and the ground wiring extending in the circumferential direction of the substrate (12, 52), wherein the substrate (12, 52) is attachable onto, and detachable from, the motor, the substrate (12, 52) characterized by having a first region on the inner circumferential portion side, a second region on the outer circumferential portion side, and a third region between the first region and the second region, the first region being annular or partially annular, the second region being annular or partially annular, and the third region being annular or partially annular, one of the power supply wiring and the ground wiring is on the first region, another one of the power supply wiring and the ground wiring is on the second region, and the first region, the second region, and the third region are on a single flat surface of the substrate (12, 52). a substrate (12, 52) that is annular or partially annular, the substrate (12, 52) having an inner circumferential portion arcuate in plan view and an outer circumferential portion arcuate in plan view; a first phase control circuit on the substrate (12, 52), the first phase control circuit being configured to control a first phase of a plurality of phases of a motor; a second phase control circuit on the substrate (12, 52) so as to be adjacent to the first phase control circuit in a circumferential direction of the substrate (12, 52), the second phase control circuit being configured to control a second phase of the plurality of phases of the motor, the second phase being different from the first phase; a power supply wiring on one of an outer circumferential side and an inner circumferential side of the first phase control circuit and the second phase control circuit in a radial direction of the substrate (12, 52), the power supply wiring being connected to the first phase control circuit and the second phase control circuit, and the power supply wiring extending in the circumferential direction of the substrate (12, 52); and a ground wiring on another one of the outer circumferential side and the inner circumferential side of the first phase control circuit and the second phase control circuit in the radial direction of the substrate (12, 52), the ground wiring being connected to the first phase control circuit and the second phase control circuit, and the ground wiring extending in the circumferential direction of the substrate (12, 52), wherein the substrate (12, 52) is attachable onto, and detachable from, the motor, the substrate (12, 52)