The electrical properties of the lanthanum-doped strontium ferrite Sr0.7La0.3FeO3-delta are studied within the temperature range 750-950 degreesC and the oxygen partial pressure range between 10(-19) and 0.5 atm. The ferrite undergoes a transition from perovskite-like to brownmillerite-like structure at an oxygen pressure of about 10(-4) atm in the studied temperature range. The observed pressure and temperature dependencies of the conductivity in the browmillerite-like form of the ferrite are related to the transition of the electron conductivity from the intrinsic regime, which is governed by the band gap of about 2 eV, to the extrinsic regime, which is controlled by the extra-stoichiometric oxygen in the brownmillerite-like phase. The brownmillerite-like phase is shown to be a mixed conductor with the oxygen conductivity level rising to about 0.3 S/cm at about 900 degreesC.