The conductivity of Ca-doped BiFeO3 ceramics varies by many orders of magnitude, depending on the oxygen partial pressure during processing. Bi1–x Ca x FeO3–(x/2)+δ ceramics are mixed oxide ion/electron conductors at 800 °C, but the electron conduction can be suppressed; when sintered and cooled in N2 from 800 °C, they are oxide ion conductors with activation energy ∼0.82–1.04 eV and conductivity ∼1 × 10–5 S cm–1 at 300 °C, comparable to that of 8 mol % yttria-stabilized zirconia. When heated in O2 at 125 bar, however, they are mainly p-type semiconductors with conductivity ∼1 × 10–3–4 × 10–5 S cm–1 at room temperature and activation energy ∼0.27–0.40 eV. The oxygen stoichiometry varies over the range 0 < δ < ∼0.016, depending on processing conditions. The semiconductivity is attributed to mixed valence Fe with < ∼3.2% Fe4+.