| 摘要 |
PROBLEM TO BE SOLVED: To sufficiently achieve both various characteristics of a memory cell transistor and a cut off characteristic of a select gate transistor in a NAND type flash memory. SOLUTION: This memory device comprises a plurality of memory cell units and a plurality of select gate transistors that have gate electrodes 5, 15, 17 formed via the substantially same, simultaneously formed, gate insulating film as a gate insulating film 4 of a memory cell, and wherein one of source/drain diffusion layers 22 is connected to a memory cell unit and the other is contacted to a bit line or a source line, and is characterized in that each select gate transistor, at the position which is equal in the depth from an interface between a semiconductor substrate 1 and the gate insulating film 4, has an equal impurity concentration of a channel region 14 in a gate length direction and has a different impurity concentration distribution of the channel region from the impurity concentration distribution of a channel region 3 of the memory cell.
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