Demands for improving fuel economy and reducing carbon dioxide emmision in automobiles have been increasing rapidly. Since the ratio of alternator loss to entire loss of automobile is high, reducing the alternator loss is effective for fuel economy improvement. The alternator loss consists of three main losses; copper loss, iron loss and rectification loss. Above all, the ratio of rectification loss to the alternator loss, which is approximately 30%, is relatively high. DENSO has developed “MOS rectifier” to reduce the rectification loss. The MOS rectifier is a commutating device which has MOSFETs as rectifying devices instead of diodes. The MOS rectifier contributes to fuel economy improvement of automobiles by reducing rectification loss with low On-Resistance(Ron) MOSFET. Since the MOS rectifier is exposed to severe temperature environment from -40 °C to 120 °C, temperature stress on solder and Aluminium wire is large. Therefore, there is concern about reliability of the connection part in conventional packaging technology such as package with ceramic substrate that is not mold. Additionaly, since over 100 A large current is applied into MOS rectifier, reducing resistance of electrical path and improving thermal resistance of MOSFET are issues. DENSO selected mold resin seal structure for MOS rectifier to improve reliability of connection part. DENSO adopted copper clip for connection between MOSFET and lead frame instead of Aluminium wire bonding to reduce resistance of electrical path, and selected heatsink-half-molded-structure to reduce thermal resistance of MOSFET which is the hottest area. DENSO has developed highly-reliable and highly-efficient MOS rectifier with the packaging technologies.