a semiconductor integrated circuit has an applied external voltage detector which determines if a level of an applied external voltage exceeds a threshold level . when the applied external voltage does not exceed the threshold voltage , an internal voltage selector selects and outputs to a voltage drop circuit a constant reference voltage which is generated and dropped from the applied external voltage by a reference voltage generator , based on an output of the applied external voltage detector . the voltage drop circuit generates and applies an internal voltage equal to the constant reference voltage , i . e . a dropped applied external voltage to internal circuit . on the other hand , when the applied external voltage exceed the threshold voltage , the internal voltage selector selects an aging voltage output from an aging voltage generator , based on an output of the applied external voltage detector . the aging voltage is higher than the constant reference voltage , and is dependent upon the applied external voltage . an internal voltage equivalent to the aging voltage is generated and applied to the internal circuit by the voltage drop circuit .