The influence of post deposition annealing (PDA) temperatures on electrical characteristics of Al2O3/InSb metal-oxide-semiconductor capacitor (MOSCAP) structures is investigated. Low frequency C-V responses with strong inversion behavior in the whole range of measured frequency (100 Hz-1 MHz) are observed, indicating very short minority carrier response time in InSb. The PDA temperature of 300oC and above would result in the reduction of maximum capacitance. At the PDA temperature of above 300oC the C-V hysteresis, frequency dispersion and stretch out increases significantly, indicating the degradation of the MOSCAP structures. The degradation might relate to the interdiffusion between Al2O3 and InSb during thermal steps.