Surface electrical properties of ZnO single crystals were measured and were correlated with complementary LEED and Auger measurements. For the crystal faces (0001), (000 1 ), (11 2 0), and (10 1 0) that were prepared by ion bombardment and anneal in ultrahigh vacuum, the above surfaces were found to be: (a) atomically regular as judged by bright LEED spots, (b) free of chemisorbates as judged by Auger spectroscopy, and (c) electrically inert, as judged by the inability of the surface to become charged when immersed in a flux of thermalized negative ions. Similar observations were made on the (0001) face, prepared only by chemical polishing in HCl. All the above phenomena persisted for remarkably extended periods without reprocessing, even after exposure to room air for 3 months. On the other hand, the (000 1 ) (11 2 0), and (10 1 0) surfaces that were prepared only by chemical polishing were found to be: (1) atomically irregular as judged by LEED, (2) nominally flat as judged by SEM, (3) contaminated with strongly bound chlorine as judged by Auger, and (4) electrically active in the following sense; when negative thermalized ions were deposited from a corona source in air, the ZnO surfaces easily became charged and a giant band bending of ≈ 70 V was sustained in the dark. On these chargeable surfaces, photodischarge spectroscopy was carried out with less-than-bandgap-light, and discrete energy levels within the ZnO bandgap of the extrinsic surface states were inferred. Depending on crystal face, the surface state levels below the conduction band were from 1.1 to 1.7 eV. On the basis of these and other observations, it was possible to deduce various bulk and surface discharge mechanisms and to correlate the charging ability with the presence of strongly bound chlorine.