The capacitance of the double-layer at the interface between irreversible (current-blocking) gold electrodes and yttria-stabilised zirconia (YSZ) was measured by impedance spectroscopy as a function of the applied electrode potential and yttria content (2–8 mol%). At moderate temperatures, 300–660 K, the dielectric constant of zirconia stabilised with 8 mol% yttria is thermally activated with an activation energy of 12.6±2.1 kJ/mol. Above 700 K, where the oxygen vacancies in YSZ are rendered mobile, contributions arise from space-charge polarisation at the blocking electrolyte/electrode interface. Based upon the Gouy–Chapman theory, a simple thermodynamic model, which takes into account the effect of site exclusion of the doubly ionised oxygen vacancies, is presented for the formed double layer. Fair agreement is obtained with the experimental differential capacitance characteristics, which show a maximum around −125 mV at 822 K. The activation energy of the dielectric constant of YSZ with 8 mol% yttria in the temperature range 700–900 K is found to be 116±34 kJ/mol.