Abstract: An integrated substrate comprising a heatsink base, and a multilayer circuit board bonded thereto, the multilayer circuit board having the capability to interconnect both power and control semiconductor elements and efficiently dissipate heat therefrom. A thermally conductive and electrically insulating bonding material having excellent thermal properties bonds the multilayer circuit board to the base. One or more thick electrically conductive foil patterns are formed intermediate the top surface of the circuit board and the heatsink base, the thick foil pattern(s) adapted to interconnect high power semiconductor elements. Also included intermediate the top surface of the circuit board and the heatsink base are one or more interconnect patterns which wire control semiconductor elements.