This semiconductor device (S1) is provided with a first external electrode (101) having an outer peripheral section (101s) which is circular when viewed from above, and which is attached to an alternator (Ot). The first external electrode (101) has, mounted thereon: a MOSFET chip (103); a control circuit (104) into which a current or a voltage 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 current or the voltage, a control signal to be supplied to a gate (103g) of the MOSFET chip (103); and a capacitor (105) for providing a power supply to the control circuit (104). A second external electrode (107) is provided to the MOSFET chip (103), at side opposite to the first external electrode. The first external electrode (101) and the first main terminal (103d) of the MOSFET chip (103) are electrically connected. Furthermore, the second external electrode (107) and the second main terminal (103s) of the MOSFET chip (103) are electrically connected.