The effect of sputtering power on the amorphous Ga 2 O 3 thin film deposited using the radio frequency sputtering system was evaluated. Amorphous Ga 2 O 3 is cheaper and more efficiently fabricated than crystalline Ga 2 O 3, and is studied in various fields such as RRAM, photodetector, and flexible devices. In this study, amorphous Ga 2 O 3 was deposited by radio frequency sputtering system and represented a transmittance of over 80% in the visible light region and a homogeneous and dense surface. The optical band gap energy decreased as the sputtering power increased owing to the quantum size effect. Thus, the specific band gap of amorphous Ga 2 O 3 can be obtained by adjusting the sputtering power, it indicates amorphous Ga 2 O 3 can be used in various fields.