Two-dimensional heat-dissipation models of common devices were established using the finite element method to improve the heat-dissipation capacity of quantum-cascade lasers (QCLs). By setting the heatsink temperature to 293K, wavelength to 8.3μm, waveguide width to 8μm, and thermal power to 12.4W, the temperature, heat flux distribution, and heat dissipation capabilities of QCLs with different device structures were studied. The results show that the highest temperatures of the epilayer-up-bonded double-channel ridge device without and with electroplated gold were 546K and 409K, respectively, while that of the epilayer-down-bonded device was 362K. For buried heterostructure (BH) devices, the highest temperatures of the epilayer-up-bonded device without and with electroplated gold were 404K and 401K, respectively, while that of the epilayer-down-bonded device was 361K. Compared with the copper submount, the highest temperature of the buried heterostructure epilayer-down-bonded to a diamond submount device was 355K. Analysis of the heat flux distribution of the models shows that the heat flux of the BH devices is more uniform, and the temperature of the core area is lower, indicating that BH structures are more suitable for high-power devices.