AlGaAs/GaAs heterojunction solar cells having conversion efficiencies greater than 19% have been produced on large‐area substrates (13 cm2) using the organometallic‐sourced VPE process. At 1 sun (simulated AM2) these devices have open‐circuit voltages of 1.01 V and short‐circuit currents of 20.9 mA/cm2. In sunlight at a flux concentration of 933 suns at AM2.1, a conversion efficiency of 19% and a fill factor of 0.757 was measured.