This two-year proposal is to implement AlGaN/GaN HEMTs with p-GaN cap with ALD Al2O3 or/and PECVD Si3N4 passivation. The activation process in Mg-doped p-GaN is an important step in device fabrication. The purpose of using p-GaN cap to replace i-GaN cap in AlGaN/GaN HEMT is to establish a p-n junction at device surface to retard carriers injecting onto surface for recombination which is similar to ledge structure in HBT. To meet two major circuits applications, RF power amplification and high-voltage power switching, two different gate structures are studied in this proposal. Both 0.2 μm Schottky gate and 2 μm MIS gate devices are designed and fabricated for p-GaN cap study and evaluation. The device performances are characterized by basic DC IV measurements and AC stress and transient measurements. The main AC stress and transient measurements including: 1. ID-VDS gate-lag, 2. ID-VDSdrain-lag, 3. Dynamic on-resistance, 4. Trap profiles, 5. [s] before and after stress measurement, 6. Using substrate bias to differentiate traps locations.