This EXMATEC 2010 paper by Morkoç, Kayis, Leach, Zhu, and Handel examines HFET stability and 1/f noise. The research presents comprehensive analysis of relationships between low-frequency noise characteristics and long-term reliability in heterostructure field-effect transistors, showing that noise measurements during accelerated aging tests reveal degradation mechanisms and predict failure modes, enabling development of reliability models and screening procedures for ensuring robust performance of GaN and other compound semiconductor transistors in demanding applications.