Due to the dependence on both bulk and interface properties neither the effective dielectric constant ε nor the leakage current J can be scaled in a straightforward manner with film thickness for high-ε thin film capacitors. Based on detailed investigations of different thickness series of (Ba,Sr)TiO3 films on platinized substrates the bulk and interfacial properties are separated. An approach to estimate the apparent interfacial layer thickness is discussed. The behavior of the leakage current is divided in two regions: for low voltages, ≤1 V, the currents are very low, ≤10-10 A/cm2, and dominated by the relaxation currents (Curie–von Schweidler behavior). At higher voltages the change to a very strong power law dependence is observed, J∼E16. The thickness dependence is removed by scaling with the internal field or dielectric displacement of the film, D=ε0εE. Hence, a direct connection between the increase in ε and the increase in leakage with film thickness is revealed. This behavior is accompanied by a larger scatter of the data and seems to be controlled by a more inhomogeneous or local conductivity. Influences of the measuring temperature and of stoichiometry and interfacial properties are discussed.