Methods of erasing data in a flash memory device are provided in which a plurality of wordline bias voltages are generated that include wordline bias voltages having at least two different levels, erasing data by applying the different wordline bias voltages to respective ones of a plurality of wordlines while applying an erasing voltage to a bulk region of memory cells, and verifying the erased states of the memory cells. Pursuant to these methods, the spread of the threshold-voltage distribution profile that may result from deviations of erasure-coupling ratios between memory cells may be reduced.