A semiconductor device comprises a semiconductor substrate (20) of one conductivity type having low resistivity, which is used as a conductive member and is mounted on a lead member (9d) held at a common electric potential, a first epitaxial layer (21) of one conductivity type having high resistivity and provided on the semiconductor substrate (20), a second epitaxial layer (22) of an opposite conductivity type provided on the first epitaxial layer (21), and at least one semiconductor layer (30) of one conductivity type having low resistivity, which reaches the semiconductor substrate (20) through both the second and first epitaxial layers (22, 21) so as to provide an electrical path to the lead member (9d) therethrough and is isolated from the second epitaxial layer (22) through a PN junction. A circuit element such as transistors and resistors is provided in each island region provided by the second epitaxial layer (22), and ground electrodes or their interconnection layers (26g) of the circuit elements are electrically connected to the semiconductor susbtrate (20) through the semiconductor layer (30), which serves as a lead member, without using a bonding wire (8d).