Abstract: 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℃ 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.