Nonvolatile semiconductor memories with a cell structure suitable for a

Abstract

A nonvolatile semiconductor memory with a unit cell structure suitable for high speed operation and a low power supply voltage. The nonvolatile semiconductor memory includes a switching circuit including block select transistors connected by its respective terminal to a corresponding bit line. This switching circuit transmits a signal only when a string to which the switching circuit corresponds is selected. A second active region having a different impurity concentration from a first active region constituting source and drain regions of memory transistors is formed at a substrate contact portion of a bit line contact portion where the memory string and bit line are connected. The impurity concentration of the second active region is lower than that of the first active region.