Abstract: The results of an experimental study of the real structure of thin films of κ-phase gallium oxide are reported. It has been established by electron backscattering diffraction in a scanning electron microscope and by transmission electron microscopy that gallium oxide single microcrystals consist of three types of rotating domains of the orthorhombic symmetry, which are rotated relative to each other around the growth axis by an angle of 120°. Single-crystal domains are characterized by a high density of straight antiphase boundaries, which, when intersecting, form a significant fraction of the domain wall structure.