AbstractDual‐junction GaAs laser power converters optimized for one monochromatic wavelength are presented, and their temperature dependence is experimentally evaluated. External quantum efficiency and irradiance‐dependent current–voltage measurements (10 to 104 W/cm2) under monochromatic laser light (809 nm) have been undertaken to quantify temperature‐ and irradiance‐dependent effects on the performance. The temperature dependence of the current matching of the two subcells, caused by the temperature‐dependent absorbance, is quantified. Losses in performance due to variations in operating temperature for different power‐by‐light applications are calculated to be between 16.2% and 21.0%. Future potential enhancements in cell performance are discussed. For elevated temperatures, super‐linear behavior of the spectral response with increasing irradiance is observed, which is attributed to effective luminescent coupling from the top to the bottom subcell as the device becomes more radiative limited. For low temperatures, where the bottom cell is overproducing, no dependence on irradiance is found, which shows the influence of photon transport losses to the substrate. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.