In one embodiment, a nonvolatile semiconductor memory device includes a plurality of memory cell transistors disposed on device regions. Each of the memory cell transistors includes a tunnel insulator disposed on a device region, a charge storage layer disposed on the tunnel insulator, and formed of an insulator, a block insulator disposed on the charge storage layer, and a gate electrode disposed on the block insulator. The gate electrode of each memory cell transistor is isolated by an insulator from the gate electrode of an adjacent memory cell transistor adjacent in a gate length direction. Further, the block insulator is disposed on the device region extending in the gate length direction, and continuously disposed in regions under the gate electrodes of the memory cell transistors and in regions between the gate electrodes of the memory cell transistors. Further, the block insulator disposed in the regions between the gate electrodes includes a thin portion which has a smaller thickness than the block insulator formed in the regions under the gate electrodes.