The authors extracted the thermal resistance RL=9.6 K/W and the electrical power dependence of the electronic temperature Re=12.5 K/W of Ga0.47In0.53As/Al0.62Ga0.38As1−xSbx quantum-cascade lasers QCLs operating at 4.9 m, in the lattice temperature range of 60–90 K. The low electron-lattice coupling constant =10.4 K cm2 /kA can be related to the beneficial effect of the high conduction band offset, peculiar to the GaInAs/AlGaAsSb material system, on the electron leakage. The authors found an active region cross-plane thermal conductivity value k=1.8±0.1 W/ Km, which is approximately three times larger than that measured in QCLs with GaInAs/AlInAs heterostructures.