The semiconductor device includes a semiconductor element, a first lead, and a second lead. The semiconductor element has an element obverse surface and an element reverse surface spaced apart from each other in a thickness direction. The semiconductor element includes an electron transit layer disposed between the element obverse surface and the element reverse surface and formed of a nitride semiconductor, a first electrode disposed on the element obverse surface, and a second electrode disposed on the element reverse surface and electrically connected to the first electrode. The semiconductor element is mounted on the first lead, and the second electrode is joined to the first lead. The second lead is electrically connected to the first electrode. The semiconductor element is a transistor. The second lead is spaced apart from the first lead and is configured such that a main current to be subjected to switching flows therethrough.