High-k oxide material with a high capacitance density, low leakage current density, high-dielectric breakdown voltage and small quadruple voltage coefficient of the capacitance is important for on-chip metal-insulator-metal (MIM) capacitors as well as gate insulators for semiconductor power devices. So in order to improve the quality of such films, a post-deposition process, such as annealing is expected to be effective. In this paper, we carried out various annealing steps after deposition of Al2O3 films with thermal ALD. The electrical characteristics of these Al2O3 films were evaluated. Annealing was proven to be effective in improving the Al2O3 film quality decrease the leakage current and the fixed charge. For O2 annealing at 400°C of MIM capacitor structures containing Al2O3 films deposited with thermal ALD using H2O at a relatively low temperature of 75°C. We achieved a leakage current density of 10-9 A/cm2 level and a capacitance density above 10fF/μm2. However, it it is necessary to improve the voltage dependence of the capacitance. For future optimization not only the post-deposition process should be investigated but also the ALD deposition itself, including the selection of the oxidizing co-reactant.