Nonvolatile semiconductor memory device and method for controlling the same

Abstract

The present invention provides a semiconductor memory device that can minimize the widening of the threshold voltage distribution of cell transistors during a data erasing operation. The semiconductor memory device includes: a memory cell unit that is formed with nonvolatile memory cells connected in series, is divided into at least two groups each including one or more of the nonvolatile memory cells, and has one end connected to a source line and the other end connected to a bit line, word lines being connected to the gates of the nonvolatile memory cells, the voltages of the word lines being controlled to store data from the bit line or output stored data onto the bit line; and a voltage applying circuit that applies voltages to the word lines of the nonvolatile memory cells, applying a first voltage to the word lines of the nonvolatile memory cells of the group located closer to the bit line, and applying a second voltage to the word lines of the nonvolatile memory cells of the group located closer to the source line, with respect to the two adjacent groups of the memory cell unit, when a data erasing operation is performed to erase data stored in the nonvolatile memory cells forming the memory cell unit, the second voltage being higher than the first voltage.