A model describing the phototransient response of a semiconductor electrolyte junction to a short laser pulse in case of "current-doubling" reactions is proposed. The rate constants of a charge transfer across the Helmholtz layer, the recombination of carriers and injection of majority carriers from intermediates in the solution back to the semiconductor are introduced in this model. The analysis is restricted by consideration of a low intensity pulse which enables perturbation caused by illumination to be neglected, and second-order processes such as the capture of the second minority carrier by the reactive intermediate which can take place under strong light illumination can be ignored. A general equation describing the phototransient response in the frame of a simple linear model is obtained, and different cases in photopotential and photocurrent measurements are considered. Analysis of phototransient data in the case of current-doubling reactions allows the rate constants of charge transfer at the semiconductor electrolyte interface to be estimated directly.