A semiconductor substrate includes: a semiconductor crystal layer grown on one face of a substrate; and a stress relaxation layer, which is formed on the other face opposite to the one face and the side face of the substrate and applies stress to the substrate in the same direction as the direction of stress which the semiconductor crystal layer applies to the substrate. In this case, stress of the semiconductor crystal layer to the substrate is offset. Therefore, warp of the semiconductor substrate and generation of cracks are inhibited.