The problem of increasing efficiency, reliability and radiation resistance of solar cells based on AlGaAs/GaAs heterostructures can be solved by using an internal Bragg reflector. The Bragg reflector as a back surface reflector and as a back surface potential barrier which allows to conserve the high photosensitivity in the long- and middle-wavelength parts of the spectrum after electron and proton irradiation. The effect of base doping and base thickness on the radiation resistance of AlGaAs/GaAs solar cells with the internal Bragg reflector has been investigated. Concentrator solar cells efficiency and related parameters before and after 3 MeV electron irradiation at the fluence up to 3 x 10(15) cm(-2) are represented. A base doping level of 1 x 10(15) cm(-3) and base thickness in the range 1.1-1.6 mum give an EOL AM0 efficiency of 15.8% (BOL-22%) at 30 Suns concentration after exposure to 1 x 10(15) cm(-2) electron fluence. This EOL efficiency is among the highest reported for GaAs single-junction concentrator cells under AM0 conditions, Making the base doping level lower and the base thinner allows retaining a j(EOL)j(BOL) ratio of 0.96 upon exposure up to 3 x 10(15)e/cm(2) 3 MeV electron fluence. These results are additionally supported by the modeling calculations of the relative damage coefficient. (C) 2001 Elsevier Science B.V. All rights reserved.