Previous work has shown that germanium oxynitride films grown on Ge substrates by thermal oxidation followed by nitridation provide a passivating dielectric which can be used to fabricate metal‐oxynitride‐semiconductor field‐effect transistors. We have investigated the interfacial microstructure of this semiconductor‐dielectric system with high‐resolution transmission electron microscopy (TEM) and show that 21‐nm‐thick germanium oxynitride films grown using this technique are uniform in thickness and interfacially smooth on a scale of ±0.5 nm over lateral peak‐to‐peak distances on the order of 100’s of nm. The germanium oxynitride was seen to be electron beam sensitive with significant damage to both the oxynitride and the semiconductor‐insulator interface being observed after exposure for 15 s to 200 keV electrons at a current density of 2.250 A/cm2at the specimen.