Abstract: The hybrid integrated circuit includes a first wiring substrate having a plurality of signal line layers and a plurality of ground conductive layers, each of the signal line layers and a corresponding one of the ground conductive layers making up a microstrip line; a cavity formed in the first wiring substrate to expose one of the ground conductive layers at a bottom of the cavity; a semiconductor chip mounted in the cavity and having a bottom surface fixed to the one of the ground conductive layers; and a mounting component mounted to an upper surface of the first wiring substrate but not above the cavity.

Abstract: A high-frequency power module is provided which has excellent heat radiating characteristics for carrying heat away from a power device element contained in the module. Also, the module can be miniaturized to a size of about 0.2 cm.sup.3 and can be inexpensively manufactured. In order to produce the module, a multilayer substrate for a high-frequency integrated circuit device is provided. The substrate contains a first substrate layer, a first metal layer, a cavity, and a first through hole. The first substrate layer has a first surface on which a first wiring layer is formed, and the first metal layer is formed at least indirectly on the first substrate layer. The cavity is formed through the first substrate layer such that an exposed portion of the first metal layer is exposed, and the first through hole is provided at the exposed portion of the first metal layer and extends through the first metal layer.