Sn‐doped ɛ‐phase dominant Ga2O3 films (ɛ‐Ga2O3 films) are grown on c‐plane sapphire substrates using metal–organic vapor‐phase epitaxy and transformed to β‐phase films by thermal annealing. The morphological and electrical properties of the phase‐transformed β‐Ga2O3 films dependent on experimental conditions are characterized. The ɛ‐Ga2O3 film is completely transformed to the β‐phase by thermal annealing to realize a high electrical conductivity while maintaining a good surface flatness. When the ɛ‐Ga2O3 films are grown, a mixing ratio of the β‐Ga2O3 component to the ɛ‐Ga2O3 film is controlled to improve the crystalline quality of the β‐Ga2O3 films transformed from ɛ‐Ga2O3 by annealing (transformed β‐Ga2O3). Compared to an as‐grown β‐Ga2O3 film, higher‐quality heteroepitaxial β‐Ga2O3 films with better electrical conductivity and surface morphology can be obtained by the phase transition method, and these results show adequate repeatability.