The reliability issues of Flash electrically erasable programmable read-only memory (Flash EEPROM) are reviewed in this paper. The reduction of the memory cell size and improvement in the reliability have been realized by several breakthroughs in the device technology; in particular, the reliability of the ETOX and NAND structure EEPROM will be discussed in detail. Flash EEPROM is expected to be a very promising device for a large nonvolatile memory market. One of the most promising applications is the replacement of the conventional magnetic hard disk by nonvolatile memories.