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We report the epitaxial growth of (010) β-(AlxGa1−x)2O3 using tritertiarybutylaluminum (TTBAl) as an aluminum gas precursor in a hybrid molecular beam epitaxy (h-MBE) system. In conventional MBE systems, a thermal effusion cell is typically used to supply Al. However, in an oxide MBE system, using a conventional Al effusion cell can cause difficulties due to the oxidation of the Al source during growth. This often requires breaking the vacuum frequently to reload Al. Our approach utilizes TTBAl, a gaseous Al source, via a h-MBE to circumvent the oxidation issues associated with traditional solid Al sources. We investigated the growth conditions of β-(AlxGa1−x)2O3, varying TTBAl supply and growth temperature. For this purpose, we utilized both elemental Ga and Ga-suboxide as Ga precursors. Controllable and repeatable growth of β-(AlxGa1−x)2O3 with Al compositions ranging from 1% to 25% was achieved. The impurity incorporation and crystal quality of the resulting β-(AlxGa1−x)2O3 films were also studied. Using TTBAl as a gaseous precursor in h-MBE has proven to maintain stable Al supply, enabling the controlled growth of high-quality β-(AlxGa1−x)2O3 films.