Thermochemical data of boron subphosphide are derived from reported decomposition data of cubic boron monophosphide BP. Both reported boron subphosphides, i.e. B 6 P and B 1 3 P 2 , are taken into account, without claiming either of these to have the reported stoichiometry. The standard heat of formation Δ f H 0 , the standard entropy S 0 , and the heat capacity as a function of temperature C 0 P , T of B 6 P and B 1 3 P 2 are Δ f H 0 = 69.2 11.4 kJ/mol, S 0 = 213 15 J/mol K, and C 0 P , T = (42.0 0.9) + (0.166 0.004) T J/mol K, and Δ f H 0 = 175 4 kJ/mol, S 0 = 462 10 J/mol K, and C 0 P , T = (87.6 1.8) + (0.359 0.008) T J/mol K, respectively.