Abstract Employing a Tian-Calvet-type calorimeter operating in the scanning mode at temperatures from 1120 to 1220 K, the enthalpy change, ΔdH, associated with the decomposition of GaBO3 (=1/2β-Ga2O3+1/2B2O3(liq.)) and the corresponding decomposition temperature, Td, were determined: ΔdH=30.34±0.6 kJ/mol, Td=1190±5 K. Using the transposed-temperature-drop method the thermal enthalpy, H(T)−H(295 K), of GaBO3 was measured as a function of temperature, T, in the region from 760 to 1610 K; the results obtained are [H(T)−H(295 K)]/(J/mol) =104.8·(T/ K )−31 300 (760 K K ), [H(T)−H(295 K )]/( J/mol )=138.8·(T/ K )−41 480 (1190 K K ). On the basis of the experimental results, the enthalpy and entropy of formation, ΔfH and ΔfS, respectively, of GaBO3 from the component oxides were derived: Δ f H=−30.34 kJ/mol, Δ f S=−25.50 J/(K·mol) at 1190 K, Δ f H=−10.55 kJ/mol, Δ f S=−5.48 J/(K·mol) at 298 K. The enthalpy versus temperature curve shows, apart from a step associated with the decomposition of GaBO3, a further step at 1593 K which is attributed to a monotectic equilibrium.