An n-type amorphous Ga2O3 thin film with a bandgap of 4.9 eV is formed using the Sn-dopant spin-on-glass (SOG) method followed by a drive-in process at 400 °C for 1 h in an Ar atmosphere. The diffused Sn dopants effectively impact the current enhancement of the amorphous Ga2O3 thin film. The metal-oxide-semiconductor field-effect transistor (MOSFET) with the Sn-doped amorphous Ga2O3 channel layer exhibits typical n-type behavior and well-behaved transistor characteristics presenting two distinct operation regions: linear and saturation. By using a low-temperature deposition method, it becomes possible to create n-type amorphous Ga2O3 thin films with a bandgap of 4.9 eV that are highly compatible with various substrates. Furthermore, ultra-shallow junction formation is achieved in the amorphous Ga2O3 thin film, which is beneficial for high performance device applications.