Solar energy is typically converted into electrical energy or collected as thermal energy. Co-generation of electricity and low-grade heat allows a more efficient use of the solar spectrum. To this end, a prototype of a high-concentration photovoltaic thermal (HCPVT) system is demonstrated. It is based on low-cost optical concentrator materials, a high-efficient, densely-packed multi-cell receiver array and a hierarchically stacked hot-water-cooling structure embedded in the receiver body. As the distance and number of interfaces between the photovoltaic cells and the cooling channels was minimized, an efficient PV-cell-cooling was achieved. Besides stabilizing PV-cell operation at elevated temperatures, the low-grade heat generated by the hot-water cooling approach can be used further in applications such as, e.g. thermal energy storage, space heating, heat-driven cooling, desalination for clean-water generation. Here, a prototype system is characterized under outdoor real-illumination conditions regarding its optical concentration and photovoltaic performance by recording illumination patterns and current-voltage traces. Furthermore, thermal characterization is carried out indoor by using a heater structure to simulate systematically the expected thermal load on the receiver module. Using 4.3 m2 collector area, average concentrations of almost 1000 suns with receiver-localized illumination hot-spots exceeding 3000 suns were achieved on the receiver plane of 53 × 57 mm2 size in a 5 × 5 array of triple-junction cells. The overall electrical efficiency reaches 32.3 % at 955 suns and a water inlet temperature of 25° C. The HCPVT concept enables large concentration × area products to maximize the energy-generation density while simultaneously providing a high thermodynamic efficiency for heat recovery.