Abstract: A motor control unit having a first semiconductor module circuit for converting an alternating current into a direct current, a second semiconductor module circuit consisting of switching elements for converting the direct current into an alternating current of optional voltage and frequency, and a control circuit for controlling the semiconductor module circuits. The unit has a case that is substantially rectangular in cross section, vertically high and laterally thin with respect to a perpendicular installation surface. Two heat sinks are disposed at the outside of the unit case at the back thereof and are thermally connected to a laminar heat plate that is disposed within the case and in contact with the heat dissipating installation surfaces of the semiconductor modules inside the unit case.