Hot-electron degradation in MOCVD-grown GaN-based HEMTs, with different gate recess depths, was monitored by flicker noise measurement. Drastic changes were observed in the flicker noise power spectral density, SV(f) and I-V characteristics when the devices were subjected to voltage stress at V D=10V for a short stress time of tS=1 minute. The degradations can be partially reverted by annealing the devices at 100°C for 20 minutes. Further stressing of the devices were performed with V G=-1.5V and VD=10V, which results in irreversible degradation in the SV(f). Detailed analyses of the data suggest that the stressing of the devices, with short tS, results in the generation of H+ at the AlGaN/GaN interface leading to the observed increase in ID, and SV(f). This can be easily annealed as the H+ has relatively low formation energy. The experimental results suggest that the H+ accumulated at the AlGaN/GaN interface may result in a network of percolation paths formed by the depression of the surface potential at the heterointerface. Motion of the H+, arising from the application of a large VD, leads to the modulation of the percolation paths of the carriers in the 2DEG resulting in large random fluctuations in SV(f). Further stressing of the devices exhibit substantial increase in SV(f) due to the generation of traps at the AlGaN/GaN interface. The experimental results demonstrate the significant impact of gate recess depths on the lifetimes of the devices.