In a CSP type semiconductor device, the invention prevents a second wiring from forming a protruding portion toward a dicing line at the time of forming the second wiring that is connected to the back surface of a first wiring formed near a side surface portion of a semiconductor die on the front surface and extends onto the back surface of the semiconductor die over a step portion in a window that is formed from the back surface side of the semiconductor die so as to expose the back surface of the first wiring. A glass substrate is bonded on a semiconductor substrate on which a first wiring is formed on the front surface near a dicing line with a resin as an adhesive being interposed therebetween. The semiconductor substrate is then etched from the back surface to form a window having inclined sidewalls with the dicing line as a center. A second wiring is then formed so as to be connected to the back surface of the first wiring exposed in the window and extend over one of the sidewalls of the window, that extends perpendicular to the dicing line, onto the back surface of the semiconductor substrate.