This paper reports a study of the electrical properties of a systematic series of InP/In0.53Ga0.47As modulation‐doped heterostructures grown by metalorganic chemical vapor deposition. Both Hall‐effect and Shubnikov–de Haas measurements are used to obtain consistent values for carrier densities and mobilities. The heterostructures are shown to display a persistent photoconductive effect at low temperatures (<80 K) which results in changes in both the carrier density and the mobility. The variation of mobility with carrier density is analyzed to show that alloy disorder and background charged impurity scattering are the dominant scattering mechanisms. Excitation across the InP band gap is shown to be necessary for the persistent photoconductivity. We propose a mechanism for this effect in which electron hole pairs created by illumination are separated by electric fields built into the heterojunction with the holes subsequently being trapped in the InP substrate.