We consider nonlinear charge transport of carriers in a photoexcited plasma in polar semiconductors. The diffusion and mobility kinetic coefficients in such conditions are obtained resorting to a nonequilibrium statistical thermodynamic approach. A generalized Einstein relation is derived for the nonequilibrium carriers (electrons and holes) for weak and intermediate electric field strengths. We discuss the effect of the irreversible evolution of the system and of the non-Ohmic behavior on such generalized Einstein relation.928649653