Nonvolatile semiconductor memory device having electrically and collectively erasable characteristics

Abstract

A semiconductor memory device has 2 word lines, a plurality of bit lines, a plurality of nonvolatile memory cells disposed at each intersection of the word lines and the bit lines, a write circuit for writing data to a memory cell located at an intersection of selected ones of the word lines and the bit lines, and a sense amplifier for reading data out of the memory cells. Further, the semiconductor memory device comprises a first unit for simultaneously selecting a block of 2 (n>m) word lines among the 2 word lines, and a second unit for not selecting a block of 2 (m>k) word lines among the 2 word lines. The second unit does not select the block of 2 word lines, and selects a block of 2 word lines prepared outside the 2 word lines when any one of the 2 word lines among the 2 word lines is defective. Consequently, redundant word lines are effectively employed, write and verify operations are stable, and thereby the yield and performance of the semiconductor memory device are improved.