β-GaS single crystals were obtained by the Bridgman-Stockbarger method. As the primary material, the compound synthesized from elemental components of Ga (5N) and S (5N) taken in stoichiometric amounts was used. Single crystals with the S-Ga-Ga-S blade growth direction along the ingot were obtained. Oxides of gallium monosulphide (GaS) were obtained by heat treatment of β-GaS in normal atmosphere. GaS plates with a thickness of 80 ’ 120 μm were subjected to heat treatment under normal conditions at 1120 K for duration varying between 1 hour and 12 hours. As a result of the heat treatment, the surface of the plates was covered with a white microdisperse layer. The composition of the obtained layer was determined from the analysis of XRD diagrams and micro-Raman diffusion spectra. The XRD diagrams were recorded using a diffractometer with the wavelength of λCuKα = 1.54060 Å. The Raman diffusion spectra were excited with Nd3+ laser beam radiation (λ = 352 nm, W = 500 mW). The crystalline structure of the oxide obtained by heat treatment of the β-GaS blades at 1200 K was determined from the XRD diagrams analysis. The diffraction lines were identified using the PDF N491362 channel.  The intense XRD lines at the angles of 2θ = 24.611º, 33.890º, 36.244º, 40.282º are identified as X-ray diffraction with the wavelength of λCuKα = 1.5405 Å from the planes with Miller indices (h k l) (1 1 0), (1 2 1), (1 1 0), (2 2 2) in Ga2O3 rhombohedral crystals and the lines located at the angles of 2θ = 11.456º, 22.958º, 34.239º, 46.900º and 73.814º correspond to the X-ray diffraction from the planes (0 0 3), (0 0 6), (0 0 9), (1 0 11) in GaS hexagonal single crystals. XRD diffraction lines well coincide with XRD reflexes of Ga2O3 layers in the form of nanowires [1, 2]. The composite structure of the GaS plate surface was analysed using Raman diffusion spectra. The wave numbers (intensity) of the lines present in the Raman spectrum are: 120.1 cm-1 (179.1), 152.1 cm-1 (253.1), 179.4 cm-1 (313.9), 206.7 cm-1 (793.3), 328.3 cm-1 (258.2), 355.1 cm-1 (392.0), 421.7 cm-1 (397.8), 483.5 cm-1 (279.1), 636.0 cm-1 (286.8), 661.9 cm-1 (381.5), 773.2 cm-1 (475.2). The vibration spectrum of β-GaS hexagonal crystal lattice is used in this work as a basis for UV light photodetectors, well known from [3, 4], and contains the diffusion lines with the wavelengths of 185.4 cm-1 (), 291.8 cm-1 (), 295.5 cm-1 () and 360.6 cm-1 () [7-9]. Since these lines are missing in the Raman spectrum, we can assume that the surface of the GaS plates is homogeneously coated with a layer of oxide. The vibration modes presented in Table 1 are in good correlation with the Raman spectra of β-Ga2O3 nanoformations well studied in literature [5-7].