A III–V nitride modulation doped field effect transistor (MODFET) layer structure grown by organometallic vapor phase epitaxy (OMVPE) on a sapphire substrate was employed for transistor fabrication. The MODFET layer structure contained a 75 Å GaN channel, 50 Å Al0.16Ga0.84N spacer, 20 Å Si doped charge supply layer, 130 Å Al0.16Ga0.84N barrier, and 60 Å Al0.06Ga0.94N cap layer. The thin channel (75 Å) was chosen to improve the carrier confinement in the channel. The fabricated MODFET’s had 0.25 μm long gates, and utilized a Au–Si alloy Ohmic metal and a Ti/Pd/Au gate metal. The measured transconductance was 40 mS/mm. From the microwave measurements on devices with 0.25 μm long gates, ft and fmax were determined to be 21.4 and 77.5 GHz, respectively. © 1996 American Institute of Physics.