In this work, the synthesis, morphology, optical and luminescence properties of Mn-doped β-Ga₂O₃ (Ga₂O₃:Mn) nanowires/nanosheets on Mn-doped GaS (GaS:Mn) substrate are studied. The aim was to obtain structures of semiconductors with layers of nanoformations (nanowires, nanosheets) from a wide energy band semiconductor such as β-Ga₂O₃ and to determine their characteristic properties. For the base material, Mn-doped GaS lamellae were chosen, which are optically transparent in the spectral region where the optical properties of Mn²⁺ and Mn³⁺ ions are manifested. Through thermal annealing, single-crystalline β-GaS plates doped with 1.3 atomic percent (at.%) of manganese (Mn) are exposed to an atmosphere enriched with H₂O vapor at a temperature of 800 °C for 6 h. As a result, the surface of these plates is covered with a composite layer consisting of crystallites of α-Ga₂S₃:Mn and β-GaS:Mn planar junctions. This composite exhibits a direct band gap of 2.88 eV and an indirect band gap of 2.55 eV corresponding to the β-GaS:Mn crystallites. Upon further increasing the temperature during thermal annealing to 850 °C and 920 °C, the surface of the β-GaS:Mn samples transform into a layer of β-Ga₂O₃:Mn nanowires/nanosheets with a band gap of 4.5 eV. Its intense green-orange photoluminescence is caused by electronic transitions within the Mn²⁺ ion.