Voltage stabilizing and voltage regulating circuits implemented in GaN HEMT technology provide stable output voltages suitable for use in applications such as GaN power transistor gate drivers and low voltage auxiliary power supplies for GaN integrated circuits. Gate driver and voltage regulator modules include at least one GaN D-mode HEMT (DHEMT) and at least two GaN E-mode HEMTs (EHEMTs) connected together in series, so that the at least one DHEMT operates as a variable resistor and the at least two EHEMTs operate as a Zener diode that limits the output voltage. The gate driver and voltage regulator modules may be implemented as a GaN integrated circuits, and may be monolithically integrated together with other components such as amplifiers and power HEMTs on a single die to provide a GaN HEMT power module IC.