Vaporization of (TIPO₃)_n and TIPO₄ was studied by high-temperature mass spectrometry. Thallium(III) monophosphate loses oxygen and transforms into thallium(I) polyphosphate, which congruently vaporizes without decomposition at higher temperatures. The standard enthalpies of formation and atomization of TIPO₃(gas) were determined: -737±28 and 1982±28 kj mol^-1, respectively.