Abstract This paper evaluates the use of nanomilling and STEM imaging to analyze failure mechanisms in sub-50 nm InP HEMTS. The devices were life tested at elevated temperatures and biases and their electrical characteristics were measured at each stress interval. Devices that were damaged were investigated further to assess the underlying failure mechanism. Advanced microscopy with sub-nm resolution was employed to examine the physical characteristics of the failed HEMT devices at the atomic scale. As the paper explains, the examination was conducted using a focused ion beam/scanning electron microscope (FIB/SEM), an Ar gas ion nanomill, and STEM imaging.