Impedance spectroscopy was used to study the oxygen/oxide-semiconductor interaction mechanism using sputtered beta-Ga2O3/SiO2/Al2O3 and beta-Ga2O3/BeO thin-layer sensor structures between 578 and 850 degrees C. The total sample resistance was composed of its bulk (R-b) and its grain boundary resistance (R-gb). While for the beta-Ga2O3/BeO sample R-gb is dominant in the entire temperature range, for the beta-Ga2O3/SiO2/Al2O3 structure at higher temperatures it roughly equals R-b The adsorption of oxygen influenced rather the grain boundary resistance than the bulk resistance. The oxygen sensitivity of beta-Ga2O3 proved to be frequency dependent; applying a certain frequency it exceeded the de sensitivity.