A frame-shaped sidewall is provided on a metallic base plate surrounding a semiconductor element arranged on the metallic base plate, which is provided with a stepped surface positioned at lower level at a portion of the base plate than a main surface of the base plate. A first dielectric plate is arranged on one side of the semiconductor element and a first circuit pattern is formed on its surface, a second dielectric plate is arranged on another side of the semiconductor element and a second circuit pattern is formed on the first and the second dielectric plate. An insulator is mounted on the stepped surface of the base plate, which forms a part of the sidewall. Power supply portions are provided including a band-shaped conductor. An interconnection is provided which connects the band-shaped conductor to the circuit pattern.