Rapid advances in high power electronic packaging require the development of new heat-sink/substrate materials. Advanced composites designed to provide thermal control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C)composites are under consideration for numerous electronic packaging applications. A new manufacturing process has been developed to produce high thermal conductivity (400 W/mK) C-C composites at greatly reduced cost (less than $50/lb). However, low CTE (0.25 × 10−6cm/cm °C) of C-C composites results in reduced fatigue life in chipon- board (COB) applications with silicon chips (CTE ≈ 2.6 × 10−6 cm/cm °C). A novel process was developed to convert the carbon matrix into the SiC matrix which retains the overall high composite thermal conductivity. This novel technology is well-suited for COB applications. Several types of coatings, such as CVD AIN, CVD Si and a polymer slurry-based low dielectric coating were applied to the C-SiC composite. Processing schemes were developed to produce crack-free coatings. Metallization of the dielectric coating was performed for the process integration with electronic devices. Thus, integrated substrates for power electronics were fabricated without the need of conventional metal/ceramic joining and associated high stresses. The properties of this new composite material for power electronics substrates are presented.