GaAsp/njunction solar cells, grown by vapor transport, frequently show a change in efficiency with light concentration that exceeds the predictions of the standard model based on diffusion limited and generation/recombination current‐voltage mechanisms. A cell was selected where the efficiency changed from 12 to 22% between 1 and 600 suns concentration or about four times that predicted by the standard model. The dark and light, current‐voltage characteristics of this cell were modeled with a trap controlled, space‐charge‐limited current diode model for the device leakage current. A good fit to the experimental data required a distribution density of electron traps, in the high‐resistancep/njunction interface region, on the order of 1018cm−3 eV−1with a minimum at 0.4 eV below the conduction‐band edge. Since the measured thickness of the high resistance region is 0.1 &mgr;m, the equivalent interface state density is on the order of 1013cm−2 eV−1.