The authors extracted the thermal resistance (R_L=9.6 K / W ) and the electrical power dependence of the electronic temperature (R_e=12.5 K / W ) of Ga _0.47 In _0.53 As / Al _0.62 Ga _0.38 As _1-x Sb _x quantum-cascade lasers (QCLs) operating at 4.9 μ m , in the lattice temperature range of 60–90 K . The low electron-lattice coupling constant α=10.4 K cm ²/ kA can be related to the beneficial effect of the high conduction band offset, peculiar to the Ga In As / Al Ga As Sb material system, on the electron leakage. The authors found an active region cross-plane thermal conductivity value k_⊥=1.8±0.1 W /( K m ) , which is approximately three times larger than that measured in QCLs with Ga In As / Al In As heterostructures.