The key parameters of GaN for use in microwave power amplifiers are presented. The electron-scattering effect of dislocations are presented for 2 DEG in HEMT devices. The use of the piezoelectric effect in designing Aly Ga1-yN/GaN HEMT structures is reviewed for a range of y.Short-gate device fabrication methods, and the device characterization, are presented. Maximum frequency of oscillation for .15 μm gates reached 140 GHz, while .3 μm gate power amplifiers reached 74% power-added efficiency at 3 GHz.