This paper derives and discusses an improved method for estimating the temperature of solar cells operating under high concentration conditions. The accuracy of this method was certified over a broad range of sunlight concentrations and operating temperatures using available experimental data related to multi-junction solar cells. This method provided more accurate estimations of cell temperature under high concentrations than the conventional V-oc-I-sc method. On-sun solar cell tests were carried out under high concentrations. The experimental data showed that the solar cell temperature, which was calculated by the improved method, increased almost linearly with the concentration ratio. A heat transfer model was established for comparison with the method. The results from both methods were in agreement. Furthermore, the thermal resistances of the solar-cell heat-sink system were also estimated using this method. (C) 2013 Elsevier Ltd. All rights reserved.