We calculate the temperature dependence of the threshold current densityJthin optimized (minimalJth) and unoptimized InAs/InGaSb superlattices. We find that the threshold current density of the unoptimized superlattice is well described byJth∝eT/T0,withT0∼32 Kfrom 25 to 275 K. This is the first microscopic calculation for these superlattices which indicates thatJthis well described by an empirical exponential form. In contrast, the threshold current density of the optimized superlattice is not well parametrized by a characteristic temperatureT0.This superlattice is only optimized between 250 and 350 K, due to the sharp structure of the intersubband absorption spectrum. We also consider the effect onJthof uncertainties in layer thicknesses. ©1998 American Institute of Physics.