To enable to manufacture multi-layer wiring boards without necessitating extensive facilities for chemical treatment or the like.

A semiconductor device comprises a wiring board and semiconductor chips mounted on the board. A method for manufacturing a wiring board includes a primary molding step for resin molding plural blocks 7a, 7b, 7c corresponding to the positions of substrate electrodes for connection with semiconductor chips 15 and connection to the outside, a plating step for forming wiring films 8a, 8b and 8c by electroless plating on the surface of the blocks 7a and 7b and 7c obtained through the primary molding step and a secondary molding step for resin molding an insulating base 16 in which the blocks 7a, 7b and 7c on which the wiring films 8a, 8b and 8c are formed respectively through the plating step and from which their specified parts are exposed.