With this paper we report on an extensive analysis of the degradation of AlGaN/GaN Schottky diodes, submitted to reverse-bias stress tests. The analysis is based on combined electrical measurements and 2D simulation. Results indicate that stress may induce a gradual increase in the leakage current of the devices. Capacitance-Voltage investigation was used as a tool for the analysis of the modifications in device structure generated during the stress tests. We demonstrate a new failure mechanism which consist in the formation of donor-like traps on the GaN-side of the AlGaN/GaN interface, and can explain the observed increase in diode leakage. 2D simulation was used to support the hypothesis on degradation, and to extrapolate the parameters of the trap responsible for the degradation process.