We report a notable improvement in performance, electron transport, and reliability of HfO2/In0.53Ga0.47As nMOSFETs using a plasma-enhanced atomic layer deposition AlN interfacial passivation layer (IPL) and NH3 postremote plasma treatment (PRPT). The interface state density $D_{{\mathrm {it}}}$ decreased by approximately one order of magnitude from $6.1 \times 10^{{\mathrm {12}}}$ to $4 \times 10^{{\mathrm {11}}}$ cm $^{{\mathrm {-2}}}$ eV $^{{\mathrm {-1}}}$ , and the border trap density $N_{{\mathrm {bt}}}$ also declined ten times from $2.8 \times 10^{{\mathrm {19}}}$ to $2.7 \times 10^{{\mathrm {18}}}$ cm $^{{\mathrm {-3}}}$ , resulting in the reduction of the accumulation frequency dispersion and eliminate the inversion hump in C–V characteristics, and thus improves the device performances. Furthermore, positive bias temperature instability stress indicates that the sample with the AlN IPL and NH3 PRPT is more reliable than the sample without any IPL and plasma treatment. During PBT stress, a smaller threshold voltage shift and less transconductance degradation were observed for the sample with the AlN IPL and NH3 PRPT. In addition, the maximum overdrive voltage for a ten-year operating lifetime increased from 0.19 to 0.41 V.