Semprius has a novel micro-cell based approach that addresses the cost, performance and reliability requirements of high concentration photovoltaic systems. A design that has a geometric concentration ratio of >1100 suns and three-junction 0.36 mm2 micro-transfer printed cells is now complete. A module efficiency of 33.9% at a direct normal irradiance of 850 W/m2 and cell temperature of 25°C has been independently validated for this design by the Instituto de Energia Solar at the Universidad Politecnica de Madrid. This is the highest measured module efficiency for any PV module, designed for commercial use. Several research, development and demonstration (RD&D) systems have been installed with these modules to collect early on-sun data and validate the technology. This paper presents module characterization and on-sun system results from a 3.5-kWp RD&D system installed at Instituto de Sistemas Fotovoltaicos de Concentracion, Puertollano, Spain by Semprius and Siemens. In addition, results from cleaning experiments and thermal performance of the system are presented from another RD&D system in Tucson. Comparisons of the performance of the Tucson RD&D system with co-located one-axis Si and fixed-tilt Si systems are also presented. Copyright © 2012 John Wiley & Sons, Ltd.