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AlGaN/GaN devices for both power and RF applications have been investigated in this work. In particular, regarding power applications, 100 V p-GaN gate transistors have been analysed both in DC and in dynamic conditions with specific attention to the high temperature behaviour.As a first step, the high temperature behaviour of the on-resistance (RON) of a reference process (STD process) has been investigated. The role of the different resistive components of the transistor has been analysed by evaluating how their relative weight changes with the temperature increase. Then, two different p-GaN process variations (process A and process B) have been proposed and compared to the STD process to show their improvement in terms of a limited RON increase at 150 °C, highlighting the relevance of an improved p-GaN gate processing.Secondly, the temperature effect on the RON-degradation induced by off-state drain voltage stress has been investigated in process B-like devices. The impact of temperature on the time required to reach a steady state degradation has been addressed, enabling the comparison of the RON degradation (RON/ RON0) at equilibrium. Tests performed on several samples have demonstrated the invariance of the RON/ RON0 ratio in the 25 °C to 150 °C range, suggesting the possibility to reduce the measurements required for dynamic-RON evaluation at different T.Finally, RF devices (featuring Schottky metal gate) have been characterized in terms of DC/RF performances and long-term reliability (through HTRB tests). Different trials with increasing aluminium content of the AlGaN barrier have been compared, showing the correlation with the maximum saturation current and the output power. Moreover, the trade-off with reliability specifications has been put in evidence.