A phase sensitive measurement technique that permits the simultaneous determination of two independent thermal properties of thin dielectric films is presented. Applying the technique results in a film's thermal diffusivity and effusivity, from which the thermal conductivity and specific heat can be calculated. The technique involves measuring a specimen's front surface temperature response to a periodic heating signal. The heating signal is produced by passing current through a thin layer of nichrome that is deposited on the specimen's surface, and the temperature response is measured with a HgCdTe infrared detector operating at 77 K. The signal that is produced by the infrared detector is first conditioned, and then sent to a lock-in amplifier. The lock-in is used to extract the phase shift present between the temperature and heating signal through a frequency range of 500 Hz-20 kHz. The corresponding phase data is fit to an analytical model using thermal diffusivity and effusivity as fitting parameters. The method has been applied effectively to 1.72 ��m films of Si0��� that have been thermally grown on a silicon substrate. Thermal properties have been obtained through a temperature range of 25��C-300��C. One unanticipated outcome stemming from analysis of the experimental data is the ability to extract both the thermal conductivity and specific heat of a thin film from phase information alone, with no need for signal magnitude. This improves the overall utility of the measurement process and provides a 'clean', direct path with fewer assumptions between data and final results. The thermal properties determined so far with this method are consistent with past work on Si0��� films. / Graduation date: 1998