A non-volatile semiconductor memory device includes: a nonvolatile memory area including gate electrodes, each including stack of a floating gate, an inter-electrode insulating film and a control gate, and having first insulating side walls formed on side walls of the gate electrode; a peripheral circuit area including single-layer gate electrodes made of the same layer as the control gate; and a first border area including: a first isolation region formed in the semiconductor substrate for isolating the non-volatile memory area and peripheral circuit area; a first conductive pattern including a portion made of the same layer as the control gate and formed above the isolation region; and a first redundant insulating side wall made of the same layer as the first insulating side wall and formed on the side wall of the first conductive pattern on the side of the non-volatile memory area.