To provide a semiconductor device having improved reliability. In a wiring board of BGA, an insulation layer has thereon a plurality of bonding leads. The insulation layer is comprised of a prepreg having a glass cloth and a resin layer not having the glass cloth. The prepreg has thereon the resin layer. The bonding leads are arranged directly on the soft resin layer and are therefore supported by this soft resin layer. When a load is applied to each of the bonding leads during flip chip bonding, the resin layer sinks, by which a stress applied to a semiconductor chip can be relaxed.