An internal voltage generator stably supplies an internal voltage in a semiconductor device. The internal voltage generator includes: a first internal voltage generating means for supplying a first internal voltage which has a level corresponding to a first reference voltage using an external voltage; a second internal voltage generating means for supplying a second internal voltage which has a level corresponding to a second reference voltage using the external voltage; and a third internal voltage generating means for supplying a third internal voltage which has a level corresponding to a third reference voltage generated based on the first internal voltage, using the second internal voltage as a power source.