Abstract: The thermal properties of semiconductor and superlattice nanostructures have recently gained more care for the following reasos. Firstly, the gradual shrink of the dimensions of devices and microelectronic circuits, which causes an increase in the semiconductor dissipative power per unit area. As a result, the thermal conductivity and reliability of the device would be important due to size effects. Secondly the design and fabrication of two-dimensional heterostructure semiconductor quantum well devices lead to the reduction of heat conduction and improvement of their thermoelectric efficiency. In this work, the thermal properties of two-dimensional semiconductor structures such as Si and Ge quantum wells is investigated regarding the phonon relaxation rates of the the umklapp scattering processes, boundary scattering, mass difference scattering and the thermal conductivity is calculated and plotted. It is seen that the thermal conductivity can be tuned by adjusting the spacer layer. Also the calculated results show that the thermal conductivity of the quantum well sample is nearly one order less than that of its bulk. Our results agree with recent theoretical and experimental data.