Provided is a high voltage generator for a flash memory device including a voltage pumping unit configured to generate a high voltage in response to a pumping clock signal, a transistor having a gate coupled to the high voltage and a source coupled to a program voltage, a voltage distributor coupled to the drain of the transistor, the voltage distributor configured to generate a distributor voltage, and a pumping clock controller configured to compare the distributor voltage to a reference voltage and to generate the pumping clock signal when the high voltage is less than a voltage substantially equal to the program voltage plus the threshold voltage of the transistor.