The invention enhances resistance to a surge in a semiconductor device having a semiconductor die mounted on a lead frame. An N type embedded layer, an epitaxial layer and a P type semiconductor layer are disposed on the front surface of a P type semiconductor substrate forming an IC die. A metal thin film is disposed on the back surface of the semiconductor substrate, and a conductive paste containing silver particles and so on is disposed between the metal thin film and a metal island. When a surge is applied to a pad electrode disposed on the front surface of the semiconductor layer, the surge current flowing from the semiconductor layer into the semiconductor substrate runs toward the metal island through the metal thin film.