A plurality of NAND cells are arranged in a cell array. In each of the NAND cells, a pair of selection gate transistors is connected in series to a plurality of memory cell transistors. An inter-gate connection trench is formed in an insulating film between layers of stacked gates of the selection gate transistors. The stacked gates are electrically connected to each other. At an end part of the cell array in the row direction, an STI area is formed, and dummy NAND cells are formed at an end part in the row direction. A dummy selection gate transistor is connected in series to a plurality of dummy memory cell transistors. No inter-gate connection trench is present in an insulating film between layers of stacked gates of the dummy selection gate transistor, and the stacked gates of the dummy selection gate transistor are not electrically connected to each other.