Initial results on 0.25 μm gate MODFET's have yielded ft=21.4 GHz and fmax=77.5 GHz. These devices have characteristics that agree with the gradual channel model dominated by the electron mobility. The AlGaN/GaN structure, grown on sapphire substrates, are polycrystalline, and thus yield low mobility (<100cm2/Vs) at low electron sheet density. Using a simple model, design optimization predicts electron sheet density values of 7.3 × 1012 cm−2 in thin, 3 nm quantum wells for single-sided doping with 5 nm spacer for use in future high frequency Al0.4Ga0.6N/In0.25Ga0.75N/GaN MODFET's with gate lengths of 0.10 μm. Double sided doping with 5 nm spacers would yield a sheet density of 1.4 × 1013cm−2 in such 3 nm quantum wells.