The forward current–voltage (I–V) characteristics of Ni/Au Schottky contacts on AlGaN/GaN heterostructures have been studied in this work. The electrical characteristics exhibited a strongly non‐ideal behavior that could not be described by the thermionic emission theory. Hence, we used a “two diodes model,” considering both the presence of the Ni/AlGaN barrier and of a second barrier height at the AlGaN/GaN heterojunction. Capacitance–voltage (C–V) measurements enabled us to experimentally determine the properties of the two dimensional electron gas (2DEG) and, hence, of the second barrier at the AlGaN/GaN interface. Following this approach, the anomalous I–V curves could be explained. Moreover, the value of the barrier height at zero‐electric field (flat‐band barrier height) was introduced and determined with this procedure, and resulted in a good agreement with literature data based on …