A wiring substrate for mounting semiconductors is provided with an insulation film, wires formed in the insulation film, and a plurality of electrode pads that electrically connect to the wires through vias. The electrode pads are provided to have their surfaces exposed to both of the front surface and the rear surface of the insulation film, and at least a part of the side surface of the electrode pads is buried in the insulation film. The insulation film is formed by forming electrode pads on the respective two metallic plates, thereafter, laminating an insulation layer and wires on the respective metallic plates to cover the electrode pad, and adhering the insulation layers to each other for integration, and thereafter, removing the metallic plates.