AbstractIn this work, we present the fabrication and analysis of a wafer‐bonded GaInP/GaInAsP//Si triple‐junction solar cell with 36.1% conversion efficiency under AM1.5g spectral illumination. The new cell design presents an improvement over previous III‐V//Si triple‐junction cells by the implementation of a rear‐heterojunction for the middle cell. Furthermore, an advanced metallodielectric rear‐side grating was used for light trapping enhancement in the silicon bottom cell that increased the silicon subcell current by 1.4 mA/cm². The external radiative efficiency was quantified to be 1.5 times higher compared to a reference device with a GaInAsP homojunction middle cell. A luminescent coupling factor of 0.46 between the middle and bottom subcell was determined. The share of recombination in the space‐charge region was experimentally shown to be insignificant as intended by the rear‐heterojunction design. Overall, the open‐circuit voltage of the middle cell increased by 61 mV compared to the previous generation. Given the established long‐term stability of III‐V and silicon‐based solar cells, these results are promising steps towards the future employment of III‐V/Si tandem solar cells.