First, a unilayer wiring board is fabricated, which has wiring layers formed in desired shapes on both sides of an insulating base member; and a metal bump formed on the wiring layer on one side of the insulating base member. Then, a desired number of unilayer boards are prepared and stacked up. On that case, the board disposed in the uppermost layer is prepared without having a metal bump. The boards are positioned and stacked up in such a manner that a metal bump of one of adjacent boards is connected to a corresponding wiring layer of the other board. Thereafter, resin is filled into gaps between the stacked boards, and insulating layers are formed on both sides of a multilayer board obtained through the above steps, in such a manner as to cover the entire surface except pad areas defined at predetermined positions on the wiring layers.