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The Schottky barrier formation between polycrystalline acceptor‐doped BaTiO₃ and high work function RuO₂ is studied using photoelectron spectroscopy. Schottky barrier heights for electrons of ≈1.4 eV are determined, independent of doping level and oxygen vacancy concentration of the substrates. The insensitivity of the barrier height is related to the high permittivity of BaTiO₃, which results in space‐charge regions (SCRs) being considerably wider than the inelastic mean free path of the photoelectrons. SCRs at any kind of interface should, therefore, be more important for the electronic and ionic conductivities in BaTiO₃ than in materials with lower permittivity. A Ba‐rich phase at the surface of reduced acceptor‐doped BaTiO₃ is also identified, which is explained by the formation of Ti vacancies in the 2D electron gas region at the surface.