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In this work, thermal properties of Al2O3, AlN, SiC as well as some of SiC die attachment materials are characterized by the laser flash method. The thermal diffusivity, specific heat and thermal conductivity were measured or calculated for the systems consisted of Al2O3 or AlN substrates and SiC structures with die-attach layers between them. The experiments for single materials were carried out within wide temperature range of 50°C ÷ 800°C in argon atmosphere. Firstly, the thermal diffusivity and conductivity of Al2O3, AlN and SiC bulk material were extracted to increase the final results accuracy within full temperature range. Then 8×8 mm2 SiC chips were attached to 8×8 mm2 Al2O3 or AlN substrates by silver-glass composition. Thermal properties of SiC - ceramics connections were measured from room temperature up to 350°C. The connection quality was investigated by X-ray microtomography. The thermal conductivity of the interfacial silver glass composition between SiC and Al2O3 decreases from 120 W/mK at room temperature to 45 W/mK at temperature of 350°C and between SiC and AlN from 270 W/mK to100 W/mK, respectively. These values strongly depend of interface quality and thickness of interfacial layer.