A flash memory having high reliability and a method for controlling the flash memory is provided for seeking stability of memory cell threshold voltage distribution. A NAND string of the flash memory has: a source-line-side select transistor; a source-line-side dummy cell; a plurality of memory cells; a bit-line-side dummy cell; and a bit-line-side select transistor. A method for controlling the flash memory includes the following step: after erasing a selected block, programming the dummy cell of the selected block into a programmed state by applying a programming voltage to a dummy word line which is connected to the dummy cell.