A NOR flash memory device configured to perform a program operation using an ISPP scheme, and comprising a plurality of memory cells, a word line voltage generator, and a scan controller is provided. A method of programming the NOR flash memory device comprising a bit scan method is also provided. The maximum number of cells that may be programmed simultaneously in the bit scan method is indicated by a scan bit number. The scan bit number may be changed by the scan controller during the program operation.