The chemical composition and structure of Ga2O3 obtained by thermal treatment (TT) in air of β-Ga2Se3 crystals were studied using the X-ray diffraction (XRD) method, Raman spectroscopy, EDX, and SEM. The surface of the Ga2Se3 crystal air annealed at 770 K is covered by β-Ga2O3 layer of microcrystallites and as well as by β-Ga2Se3 crystallites. The oxygen is non-homogeniously distributed on the surface of the 770 K annealed sample. The sample obtained by TT at 1150 K consists of nanolamella, nanotowers, and nanobars of β-Ga2O3, their size being estimated to 10–200 nm.
