Peeling of the core material in the wiring substrate of a semiconductor device is suppressed.The multi-chip substrate is divided so that the foldout direction of fiber and the dividing direction of a substrate in each of first core material of two sheets of a multi-chip substrate may accomplish an acute angle, and fiber is exposed to the end face formed of this division. When the foldout direction of each fiber of the first core material of two sheets and the extending direction of the end face accomplish an acute angle, fiber woven into first core material can be made fine. Exposure of the portion of resin comparatively weak to stress can be lessened. As a result, peeling of resin in a cutting plane can be suppressed. Since the foldout direction and the dividing direction of fiber are an acute angle, progress of peeling can be suppressed.