A semiconductor device including; a bottom plate having a laminated structure in which between a first and a second metal plates a third metal plate harder than these metal plates is clipped, a concave portion formed by removing a part of the first metal plate laminated on the surface of the bottom plate and the third metal plate laminated there under and expose the second metal plate, a semiconductor element arranged in the concave portion H, circuit board connected with the semiconductor element arranged on the surface of the bottom plate, circuit boards arranged on the surface of the bottom plate, a sidewall made of metal and fixed on the bottom plate surrounding the circuit boards and the semiconductor element, a metal lead provided so as to penetrate the side wall through an insulator, and a lid made of metal provided to block an opening formed by the sidewall.