A semiconductor device is of a PoP structure such that first electrode portions provided on a first device mounting board constituting a first semiconductor module and second electrode portions provided in a second semiconductor module are joined together by solder balls. A first insulating layer having an opening is provided on one main surface of an insulating resin layer which is a substrate, and an electrode portion, whose top portion protrudes above the top surface of the first insulating layer, is formed in the opening. A second insulating layer is provided on top of the first insulating layer in the periphery of the top portion of the first electrode portion; the second insulting layer is located slightly apart from the top portion of the first electrode portion. The first electrode portion is shaped such that the top portion is formed by a curved surface or formed by a curved surface and a plane surface smoothly connected to the curved surface.