Intersubband electron scattering transport in terahertz GaAs–AlGaAs quantum cascade lasers is analyzed, using a full 13-level self-consistent rate equation model. The approach includes all relevant scattering mechanisms between injector–collector and active region states in the cascade structures. Employing an energy balance equation which includes the influence of both electron longitudinal optical phonon and electron–electron scattering, the method also enables evaluation of the average electron temperature of the nonequilibrium carrier distributions in the device. The electron temperature is found to give a strong influence on the output characteristics, particularly at very low temperatures. The threshold currents and electric field-current density characteristics are in very good agreement with experiment, implying that the model has a strong predictive capability.