Disclosed is a flash memory device which includes a memory core, a high voltage generating circuit and a reference voltage generating circuit. The high voltage generating circuit is configured to generate a high voltage to be supplied to the memory core. The reference voltage generating circuit is configured to generate at least one reference voltage to be supplied to the high voltage generating circuit. The reference voltage generating circuit includes a first reference voltage generator configured to generate a first reference voltage in response to a supply voltage, and a second reference voltage generator configured to generate a second reference voltage in response to the first reference voltage. The at least one reference voltage supplied to the high voltage generating circuit includes the second reference voltage.