An internal voltage generator includes a comparison unit, a driving circuit and a bias unit. The comparison unit compares a reference voltage and an internal voltage and is configured to output a comparison voltage, which is based on a difference between the reference voltage and the internal voltage. The driving circuit receives the comparison voltage and an external power supply voltage and is configured to output the internal voltage to an output node in response to the comparison voltage. The bias unit receives the internal voltage and is configured to adaptively adjust a bias current that flows through the bias unit to drive the comparison unit, in consideration of a level of the internal voltage.