The theory of relaxation of highly nonequilibrium persistent photoconductivity in inhomogeneous semiconductor material has been developed. For a wide range of current carrier concentrations, the influence of the statistical properties of stochastic electrostatic potential reliefs on the kinetics of persistent conductivity has been investigated analytically and numerically. The predicted temporal dependence of the instantaneous relaxation time is consistent with the results of known experiments performed far from equilibrium and may be used for their interpretation.