The semiconductor device (S1) has a first external electrode (101) having an outer peripheral section (101s), which has a circular shape in top plan view and which is to be attached to an alternator (Ot). On the first external electrode (101) there mounted: a MOSFET chip (103); a control circuitry (104) to which voltages at or a current flowing between a first main terminal (103d) and a second main terminal (103s) of the MOSFET chip (103) is inputted and which generates, on the basis of the voltages or the current, a control signal applied to a gate (103g) of the MOSFET chip(103); and a capacitor (105) for providing a power supply to the control circuitry (104). The semiconductor device further has a second external electrode (107) disposed opposite to the first external electrode with respect to the MOSFET chip (103). An electrical connection is made between the first main terminal (103d) of the MOSFET chip (103) and the first external electrode (101), and between the second main terminal (103s) of the MOSFET chip (103) and the second external electrode (107).