This WOCSDICE 2010 paper by Handel, Sherif, Kayis, Leach, and Morkoç presents an HFET stability criterion. The research develops quantitative criteria based on 1/f noise measurements for assessing and predicting heterostructure field-effect transistor stability and reliability, showing that specific noise parameter thresholds correlate with stable versus degrading device behavior, providing manufacturers and users with practical diagnostic tools for screening devices and ensuring reliable performance in critical RF and power electronics applications.