A technique disclosed in the Description relates to a technique for improving the heat dissipation capability of a semiconductor element and the heat dissipation capability of a lead electrode without increasing the size of a product. A semiconductor device of the technique includes the following: a semiconductor element; a lead electrode having a lower surface connected to an upper surface of the semiconductor element at one end of the lead electrode, the lead electrode being an external terminal; a cooling mechanism disposed on a lower surface side of the semiconductor element; and a heat dissipation mechanism provided to be thermally joined between the lower surface of the lead electrode and the cooling mechanism, the lower surface being more adjacent to an other-end side of the lead electrode than the one end, the heat dissipation mechanism including at least one insulating layer.