a cooling structure for electrical circuit devices having a pair of cooling ducts , each having a coolant passageway therein , and an electrical circuit device housing formed by a pair of spaced apart heat transfer plates each joined to a housing side to provide a sealed housing space . an electrical circuit device is positioned in that sealed housing space and each of the pair of heat transfer plates is positioned adjacent to , and thermally coupled to , a corresponding one of the pair of cooling ducts . an electrically insulative heat transfer material is provided in the sealed housing space so as to be capable of being in contact with the electrical circuit device also therein .