A semiconductor device (10, 110, 210, 310) comprising: a device main body that is semi-annular in plan view, the device main body having at least an inner circumferential surface that is arcuate in plan view, an outer circumferential surface that is arcuate in plan view, a first end surface (13e-1), and a second end surface (13e-2), the device main body having first to fourth corner portions, the first corner portion being defined by the first end surface (13e-1) and the outer circumferential surface, the second corner portion being defined by the first end surface (13e-1) and the inner circumferential surface, the third corner portion being defined by the second end surface (13e-2) and the outer circumferential surface, and the fourth corner portion being defined by the second end surface (13e-2) and the inner circumferential surface, wherein at least one of the first and second corner portions and at least one of the third and fourth corner portions have cutout portions (14A, 14B) each including a straight portion (a) extending radially from the outer or inner circumferential surface (13o, 13i), and a curved portion (b) extending arcuately and connecting the straight portion (a) and the first or second end surface (13e-1, 13e-2), the straight portion (a) is parallel, and not aligned, with the first or second end surface (13e-1, 13e-2), and the semiconductor device (10, 110, 210, 310) is configured to be arranged adjacent to another same-structured semiconductor device (10, 110, 210, 310) to form an annular shape in plan view, so that wo mutually-facing same-shaped adjacent cutout portions (14A, 14A; 14B, 14B) of the first to fourth corner portions of the device main bodies of the two semiconductor devices form a single screw hole into which a common screw is fitted by insertion to fix the device main bodies of the two semiconductor devices to a base portion of an electric motor. a device main body that is semi-annular in plan view, the device main body having at least an inner circumferential surface that is arcuate in plan view, an outer circumferential surface that is arcuate in plan view, a first end surface (13e-1), and a second end surface (13e-2), the device main body having first to fourth corner portions, the first corner portion being defined by the first end surface (13e-1) and the outer circumferential surface, the second corner portion being defined by the first end surface (13e-1) and the inner circumferential surface, the third corner portion being defined by the second end surface (13e-2) and the outer circumferential surface, and the fourth corner portion being defined by the second end surface (13e-2) and the inner circumferential surface, wherein at least one of the first and second corner portions and at least one of the third and fourth corner portions have cutout portions (14A, 14B) each including a straight portion (a) extending radially from the outer or inner circumferential surface (13o, 13i), and a curved portion (b) extending arcuately and connecting the straight portion (a) and the first or second end surface (13e-1, 13e-2), a straight portion (a) extending radially from the outer or inner circumferential surface (13o, 13i), and a curved portion (b) extending arcuately and connecting the straight portion (a) and the first or second end surface (13e-1, 13e-2), the straight portion (a) is parallel, and not aligned, with the first or second end surface (13e-1, 13e-2), and the semiconductor device (10, 110, 210, 310) is configured to be arranged adjacent to another same-structured semiconductor device (10, 110, 210, 310) to form an annular shape in plan view, so that wo mutually-facing same-shaped adjacent cutout portions (14A, 14A; 14B, 14B) of the first to fourth corner portions of the device main bodies of the two semiconductor devices form a single screw hole into which a common screw is fitted by insertion to fix the device main bodies of the two semiconductor devices to a base portion of an electric motor.