Thin film capacitors of SrTiO3 with RuO2 top and bottom electrodes on Si substrates were prepared by radio-frequency magnetron sputtering at substrate temperatures 500 and 700 °C and at various oxygen partial pressures. The thickness of the dielectric layer was varied between 200 and 900 nm. The impedance spectra of these samples could be interpreted with an equivalent circuit comprising a resistance and two RC-parallel elements in series. The dielectric permittivity var epsilonr of the bulk grains, as extracted from the high-frequency semicircle in the Cole–Cole plot, was in the range 300–600. High oxygen contents lead to high values of var epsilonr but also increase the grain boundary resistance.