The influence of chemical parameters on electrical degradation in an AlGaN/GaN heterostructure was investigated in order to improve performance in metal-oxide-semiconductor high-electron mobility transistor devices. We first examined the influence of plasma chemistry on electrical degradation by using different plasma chemistries for the SiN capping layer opening and comparing the results. The full standard chemistry was evaluated in order to determine the impact of each gas on the degradation. Rsheet and x-ray photoelectron microscopy characterizations and simulations were performed to better understand how light elements such as helium penetrate deeply into the heterostructure and degrade its electrical characteristics. The materials used as masks were also studied. A photoresist mask and a SiN mask were compared on an AlGaN/GaN heterostructure during plasma processing. Electrical degradation was always greater in the presence of a resist due to the decomposition of the resist under the plasma causing hydrogen to be released into the plasma. Simulation of hydrogen implantation in AlGaN was also performed to understand its impact on electrical performance. © 2021 Author(s).