300 nm in thick β-Ga₂O₃ films were deposited by HF magnetron sputtering at temperature of 650 ºC and subsequently annealed at temperature of 900 ºC. Sensors with Pt contacts were produced based on these films. Structural and gas sensitive properties of β-Ga₂O₃ thin films were studied. As-deposited films demonstrated relatively low response and significant drift of gas sensitive characteristics. Subsequently annealing of films led to significant increase in responses to hydrogen-containing gases and long-term stability of gas sensitive characteristics. The responses to H₂ and CH₄ for annealed samples were ~140 arb. un. and ~38 arb. un. at operating temperatures of 600 ºC and 650 ºC, correspondingly. Changes in gas sensitive characteristics of β-Ga₂O₃ thin films are caused by refurbishment of microstructure of their surface. High temperature deposition and subsequently annealing are promising tools for optimizing the gas sensitive properties of β-Ga₂O₃ thin films for high-temperature applications.