A semiconductor device is provided, including a charge-pumping unit configured to charge-pump power voltage in every period of a pumping clock to generate pumping voltage, a first voltage level detection unit configured to detect a maximum voltage level of the generated pumping voltage, a second voltage level detection unit configured to detect a minimum voltage level of the generated pumping voltage, and a pumping clock generating unit configured to generate the pumping clock, the pumping clock having a frequency that is adjusted in response to an output signal of the first and the second voltage level detection units.