Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3&ohgr; method.SiO2and SiNxfilms are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films>100nm thick, the thermal conductivity shows little dependence on film thickness: the thermal conductivity of PECVDSiO2films is only∼10&percent; smaller than the conductivity ofSiO2grown by thermal oxidation. The thermal conductivity of PECVD SiNxfilms is approximately a factor of 2 smaller than SiNxdeposited by atmospheric pressure CVD at 900 °C. For films<50nm thick, the apparent thermal conductivity of bothSiO2and SiNxfilms decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistanceRI.At room temperature,RI∼2×10−8K m2 W−1and is equivalent to the thermal resistance of a∼20nm thick layer ofSiO2 . ©1997 American Institute of Physics.