Patent ID: 8363466

Claim:
A nonvolatile semiconductor memory device comprising: a string including a plurality of memory cells connected in series, each of the memory cells having a field effect transistor that stores information in a nonvolatile manner; a bit line connected to one end of the string; a source line connected to other end of the string; a plurality of word lines each connected to an associated one of gate electrodes of the field effect transistors; a word driver that drives the word lines; and a first power source line and a second power source line that supply a first voltage and a second voltage to the word driver, respectively, wherein the first voltage is a voltage between a third voltage of a first one of the field effect transistors that stores first information and a fourth voltage of a second one of the field effect transistors that stores second information, the second voltage is higher than each of the first, third, and forth voltages, the word driver supplies the second voltage to the word lines in a ready time when the string is not accessed, and the word driver supplies the first voltage to a gate electrode of a target field effect transistor to be accessed among the field effect transistors and supplies the second voltage to gate electrodes of other field effect transistors not to be accessed, in a read time when the string is to be accessed.