This paper reports a comprehensive analysis of temperature on DC and AC characteristics of AlN/β-Ga2O3 HEMT. As the temperature increases from 300 °C to 500 °C, the drain current (IDS) decreases by 50 %, leading to a 50 % decrease in transconductance (gm) without self heating effect. This decrease in maximum gm further resulted in a significant reduction of 49 % in the cut-off frequency (fT). Incorporating the self-heating effect, while the threshold voltage (Vth) remains unaffected, the maximum gm experiences a marked decrease. At 300 °C, the decrease reaches 58 %, while at 500 °C, the decrease is 36 %. Additionally, the saturation IDS shows a negative differential resistance phenomenon. Furthermore, the decrease at 300°Cin fT reaches 45 %, while at 500 °C, the decrease is 30 %. The main reason for the performance degradation caused by self heating effect at low temperatures is that the peak temperature at the channel of the device increases more significantly at low temperatures, resulting in a more significant decrease in mobility.