A technique for calculating the temperature of the nonequilibrium electron distribution functions in general quantum well intersubband devices is presented. Two recent GaAs/Ga(1–x)Al(x)As quantum cascade laser designs are considered as illustrative examples of the kinetic energy balance method. It is shown that at low current densities the electron temperature recovers the expected physical limit of the lattice temperature, and that it is also a function of current density and the quantised energy level structure of the device. The results of the calculations show that the electron temperature T(e) can be approximated as a linear function of the lattice temperature T(l) and current density J, of the form T(e) = T(l) + a(e–l)J, where a(e–l) is a coupling constant (~6–7 K/kA cm(–2) for the devices studied here) which is fixed for a particular device. © 2002 American Institute of Physics. \ud \u
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