A method of machining a wafer in which, at the time of grinding the back-side surface of the wafer, only a back-side surface region corresponding to a device formation region where semiconductor chips are formed is thinned by grinding, to form a recessed part on the back side of the wafer. An annular projected part surrounding the recessed part is utilized to secure rigidity of the wafer. Next, the recessed part is etched to cause metallic electrodes to project from the bottom surface of the recessed part, thereby forming a back-side electrode parts, then an insulating film is formed in the recessed part, and the insulating film and end surfaces of the back-side electrode parts are cut.