By providing a plurality of semiconductor chips that are connected in parallel and constitute one arm of an inverter; a first conductor to which a face on one side of said plurality of semiconductor chips is connected; a wide conductor to which a face on the other side of said plurality of semiconductor chips is connected; a second conductor said first conductor and second conductor are connected connected to said wide conductor; and a cooler to which through an insulating resin sheet, part of the heat loss generated in the semiconductor chips is thermally conducted to the first conductor and is thence thermally conducted to the cooler, producing cooling, while another part thereof is thermally conducted to the wide conductor and thence to the second conductor, whence it is thermally conducted to the cooler, producing cooling.