A semiconductor device (100) comprises a first resin substrate (101) on which a first semiconductor chip (125) is mounted a surface thereof; a second resin substrate (111) on which a second semiconductor chip (131) is mounted on a surface thereof; and a resin base material (109), joined to a front surface of the first resin substrate (101) and to a back surface of the second resin substrate (111), so that these surfaces are electrically connected. The resin base material (109) is disposed in a circumference of the first resin substrate (101) in the surface of the first resin substrate (101). Further, the first semiconductor chip (125) is disposed in a space section provided among the first resin substrate (101), the second resin substrate (111) and the resin base material (109) in the surface of the first resin substrate (101).