an internal power supply circuit for use in a semiconductor device includes a clamp circuit for clamping an internal voltage to a constant level . the clamped internal voltage is distributed to internal circuits of the semiconductor device through an output node . when the internal voltage rises momentarily due to noise in the internal power supply circuit due to open - circuit phenomenon , the rising internal voltage is discharged through the clamp circuit , thereby maintaining the internal voltage at a constant value . the clamp circuit includes a first transistor for discharging the output node , and a diode - connected transistor for generating a charge voltage at the gate of the first transistor . the threshold voltage of the diode - connected transistor is preferably equal to or lower than the threshold voltage of the first transistor .