In this paper we present an enhancement of punch-through voltage in AlGaN/GaN high electron mobility transistor devices by increasing the electron confinement in the transistor channel using an AlGaN buffer layer structure. An optimized electron confinement results both, in a scaling of punch through voltage with device geometry and a significantly reduced subthreshold drain leakage current. These beneficial properties are pronounced even further if gate recess technology is applied for device fabrication. Physical-based device simulations give insight in the respective electronic mechanisms. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)