The thermodynamic stability of tetragonal germanium dioxide has been characterized by measurements of the equilibrium ratios in the temperature range 830°–1020°K. Results are extrapolated to 298°K using estimated heat capacities, to give the standard thermal parameters, and to the tetragonal‐hexagonal transition point to give the free energy of formation of both modifications at that temperature. Hence, using published entropy and specific heat data for hexagonal germanium dioxide, the standard thermal parameters of this modification are computed. Sizeable crystals of tetragonal have been grown by vapor transport under near‐equilibrium conditions.