HfAlO/InAlAs metal-oxide-semiconductor capacitor (MOS capacitor) is considered as the most popular candidate of the isolated gate of InAs/AlSb high electron mobility transistor (HEMT).In order to improve the performance of the HfAlO/InAlAs MOS-capacitor,samples are annealed at different temperatures for investigating the HfAlO/InAlAs interfacial characyeristics and the device’s electrical characteristics.We find that as annealing temperature increases from 280 ℃ to 480 ℃,the surface roughness on the oxide layer is improved.A maximum equivalent dielectric constant of 8.47,a minimum equivalent oxide thickness of 5.53 nm,and a small threshold voltage of-1.05 V are detected when being annealed at 380 ℃;furthermore,a low interfacial state density is yielded at 380 ℃,and this can effectively reduce the device leakage current density to a significantly low value of 1 × 10-7 A/cm2 at 3-V bias voltage.Therefore,we hold that 380 ℃ is the best compromised annealing temperature to ensure that the device performance is improved effectively.This study provides a reliable conceptual basis for preparing and applying HfAlO/InAlAs MOS-capacitor as the isolated gate on InAs/AlSb HEMT devices.