We report on a high positive turn-on voltage (close to 2.5 V) of the gate-source leakage current in AlGaN/GaN high electron mobility transistors (HEMTs). The piezoeffect, the barrier, and channel doping result in the electron sheet concentration as high as1013 cm−2.A larger conduction band discontinuity and a larger electron effective mass (compared to AlGaAs/GaAs HEMTs) lead to a lower gate current and to a higher turn-on voltage. This means that AlGaN/GaN technology can be suitable for applications in digital and mixed-mode integrated circuits. ©1997 American Institute of Physics.