Nonvolatile semiconductor memory device and method for manufacturing the same

A nonvolatile semiconductor memory device comprising a memory cell region and a peripheral region,

• the memory cell region including:
• a plurality of first element isolation regions separating a semiconductor layer in a second direction crossing a first direction, the first element isolation regions including a first insulating film;
• a plurality of first semiconductor regions separated by the first element isolation regions in the second direction and extending in the first direction;
• and
• a first gate insulating film, a charge storage layer, a second gate insulating film, and a control gate electrode provided on the first semiconductor regions,
• the peripheral region including:
• a second element isolation region separating the semiconductor layer into a plurality of second element regions and including a second insulating film,
• wherein each of the first element isolation regions includes a first portion and a second portion provided under the first portion,
• a step is disposed between the first portion and the second portion,
• at least part of a side surface and a lower end of the second element isolation region are surrounded by the semiconductor layer.