A manufacturing method of a semiconductor device formed in a chip size package is improved to enhance a yield and reliability. A window to expose first wirings is formed only in a region of a semiconductor substrate where the first wirings exist. As a result, area of the semiconductor substrate bonded to a supporting body through an insulation film and a resin is increased to prevent cracks in the supporting body and separation of the semiconductor substrate from the supporting body. A slit is formed along a dicing line after forming the window, the slit is covered with a protection film and then the semiconductor substrate is diced into individual semiconductor dice. Thus, separation on a cut surface or at an edge of the semiconductor dice, which otherwise would be caused by contact of the blade in the dicing can be prevented.