We extracted the electronic temperatures, the thermal resistance RL=11.5 K/W, the cross-plane thermal conductivity k=2.0±0.1 W/ Km, and the thermal boundary resistance TBR=4.1–9.310−10 K/W m2 in strain-compensated Ga0.609In0.391As/AlIn0.546As0.454 quantum-cascade lasers operating at 4.78 m in continuous wave up to 15 °C and in pulsed mode up to 40 °C. Submonolayer thick InAs and AlAs layers are included in the active region to increase the conduction band discontinuity. We found that potential interface broadening caused by the insertion of these layers allows for a 43% improvement of the thermal conductivity with respect to conventional lattice-matched GaInAs/AlInAs heterostructures.