A multilayered substrate for a semiconductor device, which has a multilayered substrate body formed of a plurality sets of a conductor layer and an insulation layer, and having a face for mounting a semiconductor element thereon and another face for external connection terminals, the face for mounting a semiconductor device being provided with pads through which the substrate is connected to a semiconductor element to be mounted thereon, and the face for external connection terminals being provided with pads through which the substrate is connected to an external electrical circuit, wherein a reinforcing sheet is respectively joined to the face for mounting a semiconductor element thereon and the face for external connection terminals of the multilayered substrate body.