A semiconductor device includes a base member made of a material containing at least a thermosetting resin, and at least one semiconductor constructing body mounted on the base member, and having a semiconductor substrate and a plurality of external connecting electrodes formed on the semiconductor substrate. An insulating layer is formed on the base member around the semiconductor constructing body. An interconnection of at least one layer is formed on one sides of the semiconductor constructing body and insulating layer, electrically connected to the external connecting electrode of the semiconductor constructing body, and having a connecting pad portion, the semiconductor substrate is fixed to the base member by fixing force of the base member.