Abstract: An electronic circuit device includes a metallic member composed of a thermally and electrically conductive material and comprising a unitary mass defining a heatsink and being free of mechanical or electrical transition joints. Electronic switching devices are mounted on the member and in electrical and thermal contact therewith. A control circuit and a conductor are each mounted on the member and adjacent the switching circuit devices and electrical conductors interconnect the switching circuit devices with the control circuit. The control circuit and the conductor are thermally and electrically isolated from the metallic member. The metallic member comprises a heatsink for the electronic switching devices and a conductor for currents being switched thereby.