The influence of an N_2O plasma pre-treatment technique on characteristics of AlGaN/GaN high electron mobility transistor(HEMT) prepared by using a plasma-enhanced chemical vapor deposition(PECVD) system is presented.After the plasma treatment,the peak transconductance(g_m) increases from 209 mS/mm to 293 mS/mm.Moreover,it is observed that the reverse gate leakage current is lowered by one order of magnitude and the drain current dispersion is improved in the plasma-treated device.From the analysis of frequency-dependent conductance,it can be seen that the trap state density(D_T) and time constant(τ_T) of the N20-treated device are smaller than those of a non-treated device.The results indicate that the N_2O plasma pre-pretreatment before the gate metal deposition could be a promising approach to enhancing the performance of the device. The influence of an N 2 O plasma pre-treatment technique on characteristics of AlGaN / GaN high electron mobility transistor (HEMT) prepared by using a plasma-enhanced chemical vapor deposition (PECVD) system is presented. After the plasma treatment, the peak transconductance (g_m ) increases from 209 mS / mm to 293 mS / mm. Moreover, it was observed that the reverse gate leakage current is lowered by one order of magnitude and the drain current dispersion is improved in the plasma-treated device. Flash the analysis of frequency -dependent conductance, it can be seen that the trap state density (D_T) and time constant (τ_T) of the N20-treated device are smaller than those of a non-treated device. The results indicate that the N 2 O plasma pre-pretreatment before the gate metal deposition could be a promising approach to enhance the performance of the device.