An electrode for the electrochemical production of ozone, which has the compositional sequence Si/TiOx/Pt/TiO2 (TiOx is titanium oxide), was fabricated by sputtering TiO2 thin film (the thickness is typically 300 nm) on a Si/TiOx/Pt substrate. The TiO2 thin film was characterized by X-ray diffraction, transmission electron microscopy, UV photoelectron spectroscopy, UV-visible spectroscopy, and photoelectrochemical measurements: It is an n-type semiconductor of the rutile-type TiO2. The electrochemical ozone production (EOP) was realized, and a high current efficiency of 9% was achieved at a low current density of 8.9 mA cm(-2) in 0.01 M HClO4 at 15 degrees C. The observed high efficiency of EOP was considered to originate from the electrocatalysis of the n-type TiO2 in the dark when a large anodic bias was applied in which, based on the band structure of the n-type TiO2/HClO4 solution interface, electron tunneling can take place through a deep depletion layer of the TiO2 surface.