Abstract: A three-phase bridge circuit includes two sets of transistor/diode assemblies in which the diode of each assembly is connected in reverse current mode across the main current path of its transistor. Each diode of one set has its cathode connected to a positive d.c. input bus bar and its anode to a respective a.c. output bus bar. Each diode of the second set has its cathode connected to a negative d.c. input bus bar and a respective a.c. output bus bar. An input terminal has a plurality of electrical contacts, each connected to the control electrode of a respective transistor in the transistor/diode assemblies. A heat sink has its electrically insulating layer on one major surface thereof and in thermal contact therewith. Each transistor is in thermal contact with the heat sink by way of a bus bar part, and each of the bus bar parts is secured to the insulating layer so as to be in thermal contact with the heat sink.