A semiconductor device includes a comparator, an internal voltage generator, a control signal generator, and a selector. The comparator may compare a reference voltage to an internal voltage and output a comparison signal. The internal voltage generator may generate and output the internal voltage in response to the comparison signal. The control signal generator may generate a control signal. The selector may receive first and second target voltages, and select and output one of the first and second target voltages as the reference voltage in response to the control signal.