AlGaN/GaN HEMT is the forefront of semiconductor research because of its exciting physical properties and it is the choice of suitable candidate for high power electronic innovations. In general, the AlGaN/GaN can operate at higher voltages and these high bias conditions induce high electric field within the device structure that leads to degradation in the device performance. Therefore, reliability is an important issue for the device that should be analyzed properly to make it more applicable for practical applications. In this paper, we have analyzed some of the degradation mechanisms such as self heating, charge trapping etc., that affects the reliability of HEMT. It is also reported the effect of these degradation mechanisms in transistor characteristics such as mobility, threshold voltage, drain current and gate-drain capacitance. © 2012 IEEE.