In this study, the properties of high-k/InSb are verified. The gate dielectrics including Al2O3 and HfO2 are used for studying. The band alignment of Al2O3/InSb and HfO2/InSb are estimated using x-ray photoelectron spectroscopy spectra and Fowler-Nordheim (F-N) current-voltage (I–V) characteristic. The effect of annealing temperatures on the electrical properties of the MOSCAPs is also studied. It is found that the In, Sb out diffusion into high-k would be a major reason to degrade the electrical properties of high k/InSb structures.