Open‐circuit voltage characteristics of InP‐based multiple‐quantum‐well (MQW) solar cells are studied experimentally and theoretically. Experimental results are presented for spectral response and terminal characteristics of In0.53Ga0.47As/InP MQW cells and compared with results from a corresponding bulkp‐i‐ncontrol cell. Open‐circuit voltages measured for these cells, and for other InGaAs/InP and InAsP/InP MQW cells reported in the literature, are then analyzed using a simple ideal theory for MQW cells which attributes open‐circuit voltage reductions to increased radiative recombination in the quantum wells. The large (0.19–0.33 V) measured open‐circuit voltage reductions which accompany introduction of the quantum wells are shown to agree with predictions from the ideal theory to within ∼0.03 V on average. Finally, implications of this work for the design of efficient InP‐based MQW solar cells are discussed. ©1996 American Institute of Physics.