Organosilicon polymer-derived ceramic (PDC) materials have been extensively studied for their various properties such as mechanical, chemical and electrical properties. One of the least explored properties of PDC is their thermal properties, required for designing a heat energy converter. In this work, a commercially available polydimethylsiloxane elastomer is used as starting polymeric precursor. Pyrolysis of cross-linked gels conducted in inert atmosphere above 1000 °C yielded silicon oxycarbide SiOxCy, as revealed by X-ray diffraction analysis. The complex shapes of the gels are retained even after pyrolysis up to 1500 °C, however a linear shrinkage ratio of 25–30% is observed. Both thermal and electrical conductivity of free carbon based SiOxCy residues are found to rise simultaneously as the heat treatment temperature increased. The sample heat-treated at 1500 °C exhibits the room temperature thermal conductivity of 2.24 Wm-1K-1 and electrical conductivity of 0.021 S cm-1. These properties of PDCs suggest their appealing applications as a functional material in thermoelectric devices.