Thin polymorphic gallium oxide films were grown on c-plane sapphire using pulsed laser deposition. The stacked thin films (ϵ-Ga2O3 and β-Ga2O3) were sequentially grown under the same conditions but in a different ambience. Our X-ray diffraction measurements and transmission electron microscopy images confirmed a β-Ga2O3/ϵ-Ga2O3 polymorphic heterostructure with rocking-curve widths of 1.4° (β-Ga2O3 (603)) and 0.6° (ϵ-Ga2O3 (006)). The crystallographic orientation relationships between c-plane sapphire and the heterogeneously nucleated ϵ-Ga2O3 buffer layer, as well as between the ϵ-Ga2O3 and β-Ga2O3 heterogeneous layers, were determined. Our study will aid in developing novel deep-ultraviolet optoelectronic devices, such as solar-blind and metal-insulator-semiconductor deep-ultraviolet photodiodes.