GaAs solar cells with conversion efficiencies as high as 14% at AM1 have been grown by the GaCl/AsH3hydride technique. Thin (∼200 A˚) layers of InGaP were used to passivate the GaAs top surface. We observe a 70‐fold increase in photoluminescence intensity of the GaAs after passivation, which is consistent with a lowering of the GaAs surface recombination velocity from ≳106to <104cm/sec. Short‐circuit current densities (Jsc) as high as 22 mA/cm2and open‐circuit voltages as high as 0.96 V were observed. (If achieved together, those values would yield an efficiency of almost 18%.)Vocwas observed to increase directly withp‐layer thickness (t), whereasJscdecreased directly witht. The efficiency also increased as the zinc doping was decreased.