III-V wide bandgap disruptive technology is firmly positioned as a leader for high power segments operating at high frequency or under switching mode. Still, it is needed to investigate these transistors to push the maturity towards higher levels and to address elevated junction temperatures. Concerning analog RF applications, more than two decades of studies lay the main technological process basis for both obtaining improved RF performances and reliability. However, if failure signatures and their associated defects are now issues likely to be understood as individual problems, the global failure behavior still poses challenges to overcome. This paper is a contribution to the failure analysis studies on GaN technologies by providing a methodology for ensuring the validity of the stress analysis, to the accurate identification of the involved defects; this procedure is suitable even for a single stress test campaign, when usually several accelerated life tests are needed to separate concurrently proceeding effects. This methodology is based on the use of destructive and non-destructive characterization techniques, as well as electrical modelling. Key degradation processes are highlighted from different feedback studies, still considering the need of a secure procedure to avoid any misunderstanding about the origin of the tracked DC or RF variation of the devices under test.