This research highlight an innovative method for calculating the optical band gap of thin layers of aluminum oxide resulting from the surface oxidation of non‐transparent samples of aluminum. The aluminum samples were prepared using the compressing and annealing methods. Thermal heating in suitable oven was used for annealing procedures. The effects of annealing temperature on structural and optical properties of studied samples were investigated by measuring the optical band gaps and FT‐IR spectra. The results show that the annealing temperature affects the structural and optical properties of the surface layer. In addition, it was found that in the case of annealing temperature at 1000°C, the optical band gap of alumina samples was found to be 4.99 and 4.19 eV at annealing times of 2 and 4 hours respectively. On the other hand, at the temperature of 500°C, the surface has metallic properties because the area of the oxide layer is very small. This indicates that the annealing temperature has great role in determining the properties of the surface layer.
