The effects of operating temperature and the interfacial thermal resistance on device are researched by using a two-dimensional numerical simulator. A comparison between the simulated results and the experiment data demonstrates that hot electrons make a significant contribution to the negative differential output conductance which will increase with the increase of the work temperature under low drain voltage, and under upper drain voltage, the self-heating effect is an important factor to the current collapse which will become more serious with the work temperature and interfacial thermal resistance inereasing.