Porous SiC/SiO2/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated with SiO2. As a pre-treatment, the samples were either heated at 100 A degrees C or kept at room temperature followed by sintering in the temperature range 1200-1800 A degrees C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were investigated. Pre-treatment at room temperature followed by sintering up to 1800 A degrees C produced composites exhibiting a greater size of carbon crystallites, a higher ordering of the microstructure of carbon and beta-SiC and a smaller amount of SiO2, resulting in electrical and thermal conductivities of 1.17 x 10(4) Omega(-1) m(-1) and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the composite to 1.82 g/cm(3). In contrast, the pre-treatment at 100 A degrees C produced composites possessing a lower thermal conductivity of 2 W/mK.