Among commercial photovoltaic technologies, concentrating photovoltaics (CPV) has the highest solar energy-to-electricity conversion efficiency; however, CPV electricity costs are still higher than thin film or silicon PV costs, mainly because of the additional components needed (optics, tracker) and the very high price of III-V multi-junction solar cells. To date, most commercial CPV systems operated at maximum concentrations of about 500 suns; but even at this concentration level, multi-junction cells retain a significant contribution to the total cost of the system. Further increasing the concentration ratio seems an interesting route for decreasing CPV electricity costs since the efficiency of concentrator cells theoretically increases with increasing illumination levels whilst the part of the solar cells in the total system cost decreases. In this work, single, dual and triple-junction III-V solar cells designed to operate at concentrations of only a few hundred suns have been characterized under natural sunlight concentrated up to about 3000 suns. The cells were not damaged by the various series of measurements; furthermore, the electrical power delivered by the cells was found to increase with increasing concentration up to its maximum value despite the decrease in conversion efficiency observed above 200-300 suns. Calculations were also performed to complement the experimental results: the importance of optimizing the cell grid layout for ultrahigh concentration was first illustrated and finally a cost analysis suggested that a non-negligible decrease of solar electricity costs could result from increasing the concentration ratio used in commercial CPV systems. (C) 2011 Elsevier Ltd. All rights reserved.