In situ NH3 plasma nitridation was utilized to passivate InP surface, HfLaOx film was grown by plasma enhanced atom layer deposition method, and the HfLaOx film remain amorphous after 500°C annealing. High-resolution transmission electron microscopy (HRTEM) images showed that in situ NH3 plasma nitridation process make the boundary between InP and HfLaOx smooth and sharp, and could suppress the formation of the interfacial layer. X-ray photoelectron spectra (XPS) results indicated In-N and P-N bonds were formed on the nitride InP surface. The electrical measurements indicated in situ NH3 plasma nitridation process reduced the hysteresis improved capacitance density and to 7 mV, a sharp transition from depletion to accumulation was observed, the interfacial density states (Dit) of the sample with nitridation was 1.67×1012 cm2 eV1, and the equivalent oxide thickness (EOT) was 0.6 nm. The leakage current was 1.5 mA/cm2 at Vg-Vfb=1V.