[en] Study of thermodynamics of chemical equilibrium between YBa₂Cu₃O_7-δ and gas phase taking into account contribution of oxide electron-hole system is carried out. Several models of electron structure with rather wide (the width is much above kT) valence band are considered. To describe interaction of basic plane oxygen ions various approximations, allowing for short-range order, are used. Electron-hole contribution to thermodynamics of 123 oxidation is shown to be significant. Study of equilibrium allows to get information not only on ion system, but on electrons and holes of the composition