The transverse thermal conductivities of SiO2 thin films are determined as a function of film thickness. The results indicate that the apparent thermal conductivities of SiO2 thin films are much lower than the thermal conductivity of bulk SiO2. In addition, a slight decrease in the thermal conductivity is observed as the average temperature within the dielectric film increases. The average transverse thermal conductivity decreases drastically as the film thickness is reduced. This strong thickness dependence is explained in terms of an interfacial thermal resistance that develops at the SiO2/Si interface. The experimentally determined value for the interfacial thermal resistance, Rint, is 2.05 mm2 °C W-1.