The photogeneration of holes in aggregate photoreceptors has been investigated as a function of electric field, temperature, and excitation wavelength. The experimental results are describable by the Onsager theory. The fraction of absorbed photons that produce thermalized electron‐hole pairs is 0.58 and is independent of wavelength and temperature. At room temperature, the pair separation distance is 44 A˚. This distance is independent of wavelength and increases linearly with temperature. It is concluded that the photogeneration of free carriers can be explained by the surface dissociation of a thermalized exciton.