A method for generating a security feature of a flash memory includes determining a memory block from a plurality of memory blocks in the flash memory; erasing data of the determined memory block of the flash memory; providing a predetermined voltage to the determined memory block to obtain a plurality of corresponding threshold voltages of a plurality of cells in the determined memory block, wherein each of the corresponding threshold voltages corresponds to a characteristic of each cell in the determined memory block; and establishing a security feature based on the plurality of corresponding threshold voltages.