According to the present disclosure, a method of manufacturing a semiconductor device includes the steps of (a) preparing a lead frame including a switching element die pad, a control element die pad, and a third-side side rail portion, (b) mounting a switching element and a diode element on the switching element die pad and mounting a control element configured to control the switching element on the control element die pad, (c) sealing the switching element, the diode element, and the control element with a mold resin such that the power side terminal, the control side terminal, and a part of the third-side side rail portion protrude outward, and (d) forming a third-side side rail terminal by cutting the third-side side rail portion, the third-side side rail terminal extending from a part of the third-side side rail portion.