A method is disclosed for forming an aluminum oxide film on a semiconductor device. In a process of depositing an aluminum oxide film by atomic layer deposition method using TMA (trimethyl aluminum; Al(CH3)3) as an aluminum source and H2O as an oxygen reaction gas, the disclosed method supplies a NH3 reaction gas at the same time when an aluminum source is supplied. Therefore, it can increase the growth rate of an aluminum oxide film and can also improve the characteristic of preventing penetration of hydrogen into an underlying layer or a semiconductor substrate. Thus, the disclosed method can prevent degradation in a charge storage characteristic in a capacitor and lower in an electrical characteristic of various elements, thus improving an overall characteristic of a semiconductor device.