Abstract: A power electronic interposer (10) for mounting a number of power transistor integrated circuit dice (14) can be made from a multi-layer ceramic process to provide an aluminum nitride body (11) having internal tungsten traces (30-35) to electrically connect die bond pads (17,18) to interposer contact pads (25,26) allowing connection to circuitry off of the interposer. The traces can include one or more groupings of parallely spaced apart conductive vias (30,31) that are connected in an electrically parallel manner to reduce electrical resistance and inductance in the circuitry. A network of cooling conduits and optional resistance temperature detector traces can be run through other parts of the body to provide controlled active cooling. The interposer can be formed separate ceramic bodies bonded together, to package the dice.