This semiconductor device comprises a semiconductor package having a first wiring substrate and a semiconductor element disposed or mounted thereon, a mounting second wiring substrate, and a protrusion electrode terminal and a receiving terminal portion for connecting an external connecting terminal of the semiconductor package and an external connecting terminal of the second mounting wiring substrate. The protrusion electrode terminal coated with a conductor layer is disposed on the external connecting terminal of the semiconductor package. An aggregated electrode layer having a plurality of fiber electrodes that are bound or tangled is disposed on the external connecting terminal of the mounting wiring substrate. The protrusion electrode terminal on the semiconductor package side is detachably inserted into the aggregated electrode layer on the mounting wiring substrate side. Thus, the protrusion electrode terminal and the aggregated electrode layer are mechanically secured and electrically connected. Consequently, the semiconductor device has high mounting reliability without need to use solder. Thus, the cost of the material of the semiconductor device can be reduced and the number of fabrication steps thereof can be decreased.