We consider an excitonic model in which the electron is localized in adorbital on a metal site, and the hole is in a linear combination ofporbitals on the surrounding oxygen sites, with both electron and hole in an insulating LaO, Bao, etc. layer adjacent to a metallic CuO2or BiO2plane. This mechanism appears to provide a natural and consistent interpretation of high‐temperature superconductivity in both the cuprates and bismuthates.