The depth of depletion layer and height of energy barrier on ZnO non-polar surface were measured under hydrogen from the electrical properties of ZnO-ZnO contact. In capacitance measurement, it was observed that the depth of the depletion layer increased reversibly at 298 and 373 K, while it decreased irreversibly at 473 and 573 K. The increments of the depth at 298 and 373 K were nearly fitted to Freundlich isotherm, and it was suggested that donor type adsorbed states were in thermal equilibrium with other species. The height of the energy barrier on the surface from the inflection of V-I characteristics increased under hydrogen at 298 K. Typical values of the two measurements at 67 Pa hydrogen and 298 K were 40 nm (corresponding to 2.2 x 10(14) anion states m(-2)) for the depth and 5 meV for the height.