The rates of photoinduced electron transfer from p-InP to Fe(CN)64-/3- acceptors in aqueous electrolyte have been determined as a function of the initial potential drop (Le., band bending ( VBO)) in the semiconductor space charge layer using femtosecond luminescence up-conversion techniques. The effects of electric field on electron transfer were separated from the effects of field-enhanced charge separation and surface recombination through a rigorous numerical solution of the coupled continuity and Poisson equations using a Cray supercomputer. A very strong dependence of the electron-transfer velocity (Set) on VBO was found, Set reached a saturation value of 5 X lo7 cm/s when the initial value of VBO in the dark was 10.5 eV. When the initial value of VBO was set near zero, Set was 9 X lo3 cm/s. Hot electron injection processes appear to play a role in this behavior.