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.