AbstractWe present normally‐off AlGaN/Gan power tunnel‐junction FETs (TJ‐FETs) with high breakdown voltage, low off‐state leakage current and low specific on‐resistance. The TJ‐FETs exhibit normally‐off operation in an otherwise normally‐on as‐grown sample owing to a current controlling scheme different from the conventional FETs. The high 2DEG density in AlGaN/GaN heterostructure results in a thin tunnel barrier whose effective thickness is controlled by an overlaying gate electrode. This tunnel junction is controlled by an overlapping gate and deliver highly efficient quantum tunnelling, enabling normally‐off operation. A positive gate bias results in a nanometer‐thick barrier with high tunnelling current, while a zero gate bias leads to a thicker barrier that effectively blocks the current flow. High tunnel current (326 mA/mm), low off‐state leakage (10‐8 mA/mm) and high off‐state breakdown voltage (557 V) are obtained on a standard GaN‐on‐Si platform featuring a 1.8 μm buffer. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)