An Al2O3 film was prepared as a dielectric layer for an InSb material via the atomic layer deposition technique, the MIS device was developed, and the effects of annealing temperature on the post-metallization interfacial characteristics were investigated. Moreover, the interface of the MIS device was characterized using the C-V test. The results indicate that the Al2O3 dielectric layer introduced surface-fixed positive charges, and annealing processing at 200 and 300°C can effectively reduce the slowing density. Furthermore, Terman’s method can be used to obtain the interface states density distribution. This indicates that 200℃ annealing can significantly decrease the interfacial density close to the center of the bandgap and the conduction band. Additionally, negative charges being trapped near the interface of the Al2O3 dielectric layer is found to be the main cause of C-V curve hysteresis. Experiments prove that an annealing process at 200℃?300℃ can effectively improve the InSb/Al2O3 interface quality.