Semiconductor device

This invention relates to a resin encapsulated semiconductor device with lead frame. The purpose of the present invention is to provide: a resin encapsulated semiconductor package, which uses leads (lead frame), enhances heat conducting properties and prevents breaking of bonding wire, reduction in service life of solder joints and crack of a resin while ensuring reliability on strength. The solution means is: a lead material using a material containing as a main constituent material a composite alloy of Cu2O and Cu, which has a thermal conductivity as high as that of copper alloys having been conventionally used, and which is sintered to have a small linear expansion coefficient as compared with such copper alloys.