Dynamic resistance of AlGaN/GaN Metal-Insulator-Semiconductor- High Electron Mobility Transistors (MIS-HEMTs) has been extensively investigated lately because of its great impact to the energy efficiency of the devices. There have been many reports on the observation of degradation of dynamic on-resistance (Ron) after an off-state stress. Lots of efforts have also been devoted to the understanding of this phenomenon. To date, charge trapping in the buffer layer and surface states are considered the two major mechanisms for the degradation. However, a clear physical model for the degradation remains to be sought. In this study, the degradation and recovery of Ron after various stress voltage and time are investigated and correlated to the charge trapping and detrapping near the channel region.