In a semiconductor device having a package structure in which lead terminals connected to electrodes on both of the upper and lower surfaces of a semiconductor chip are exposed from both of the upper and lower surfaces and side surfaces of a sealing body formed of resin, electrodes of the semiconductor chip and the lead terminals are connected by Pb-free connection parts each having a configuration of connection layer/stress buffer layer/connection layer. In each connection part, the connection layer is formed of an inter-metallic compound layer having a melting point of 260.degree. C. or higher or Pb-free solder having a melting point of 260.degree. C. or higher, and the stress buffer layer is formed of a metal layer having a melting point of 260.degree. C. or higher and having a function to buffer the thermal stress.