Heterojunction solar cells consisting ofpGa1−xAlxAs&sngbnd;pGaAs&sngbnd;nGaAs are grown by liquid‐phase epitaxy and exhibit power conversion efficiencies of over 16% (corrected for contact area) measured in sunlight for air mass 1 at sea level, while efficiencies of 19–20% are obtained for an air mass value of 2 or more. The improved efficiencies compared to conventional homojunction (Si and GaAs) cells are attributed to the reduction of series resistance and the reduction of surface recombination losses resulting from the presence of the heavily doped Ga1−xAlxAs layer. Open‐circuit voltages of 0.98–1.0 V and short‐circuit currents of 18–21 mA/cm2(corrected for contact area) are observed for a solar input intensity of 98.3 mW/cm2.