Abstract: A plurality of individual semiconductor diode wafers secured to the rotor of a synchronous machine rectify AC from an excitation power source to provide DC to the main rotating field element. The diode wafers, connected as either a half wave or a full wave rectifier, are contained within a housing to form a rectifier assembly. The assembly is mounted directly on an inner surface of the housing carried on the shaft of the machine. The assembly is provided with suitable passageways or surfaces for flow of a non-electrically conductive cooling medium. In one embodiment, the cooling medium, as oil or air, traverses the surface of the diode wafers to provide high efficiency heat removal. In another embodiment the cooling medium traverses a heat sink on which the wafers are mounted to provide a high efficiency heat removal.