Smooth nanometer-scale films of anatase TiO2 on indium-tin oxide substrates (ITO) are obtained by electron-beam evaporation of reduced TiO2 powder. Mott-Schottky analysis shows an abrupt change in slope when the depletion layer reaches the TiO2/ITO interface. An electrostatic model is derived, which gives a quantitative description of the observed change in slope. From the potential at which the slope changes, the dielectric constant of anatase could be accurately determined. A value of 55 is found, which is significantly lower than those reported for anatase TiO2.