PURPOSE: To draw out the characteristics of a semiconductor element to the exterior without causing such undesirable phenomenons as an impedance non- alignment and a resonance, etc., by a method wherein the length of a metal radiating plate is made shorter than that of an insulated substrate.

CONSTITUTION: Internal input-output matching circuits 23 and 24 provided with integrally combined internal matching circuits and input-output terminals in one body are formed on the top surface of an insulated substrate 21 for attaching a metal radiating plate 26 utilizing metal films 25. The length of the insulated substrate 21 is made longer than that of the metal radiating plate 26 in the longitudinal direction on the input-output terminals. A semiconductor element 29 is mounted on the metal radiating plate 26, the electrode of an element 29 and metal circuits 23 and 24 are connected by metal wires 30 and a cap 27 is put on in order to obtain a semiconductor device. The device is installed on a mounting substrate 31 and connected by metal wires 35 and 36 for drawing out the characteristics of the semiconductor element to the external circuit. The void which is yielded between the package and the mounting substrate 31 can be lessened and factors which cause such undersirable phenomenons as a non-alignment and an oscillation can be removed.