Electrical measurements of the space-charge region of TiO2 single crystals (rutile) reduced in a hydrogen atmosphere were performed to assess the semiconducting properties of the material prepared with reduction time. For this purpose a rectifying TiO2/Au junction was prepared by ion sputtering, with a rear ohmic contact of InGa alloy. Impedance-spec troscopy measurements were used to investigate the Schottky character of the TiO2/Au junction and provide new data on charge-carrier density for single-crystal rutile TiO2. Semiconductors initially prepared by H-2 reduction do not show typical Schottky behavior. The electrical characteristics of these initial samples indicate coverage by an insulating surface layer, and infrared spectroscopy measurements suggest that the layer might consist of OH terminal groups. The insulating layer seemed to be decomposed either by further air oxidation followed by a second reduction step, or by intensive water photoelectrolysis, thus yielding characteristic Schottky diodes.