A high-efficiency photovoltaic conversion system based on spectrum splitting of concentrated light to fall on GaAs and Si cells placed inside light confining cavities is described and experimental results are reported: 29.4% at 180 suns (near AM1.5 direct spectrum), 22% contributed by the GaAs cell. The short-circuit current gain derived from the use of the cavities is 7-8% (relative increase). However, the system is believed to have immediate potential to achieve as much as 32% efficiency. Benefits compared to systems based on stacked cells are pointed out: (a) conventional cells based on developed fabrication techniques can be used, with minor design changes, (b) cell design can be independently optimized with the aim of achieving maximum efficiency, (c) cells can operate at different concentrations, (d) electrical power can be extracted independently from each cell, and (e) it is easy to make the electrical connections to each cell.