Silicon nitride has a high intrinsic thermal conductivity competing with aluminum nitride.However,the thermal conductivity of silicon nitride ceramics is far less than that of aluminum nitride ceramics sintered at similar condition.The main difference on the microstructure of the ceramics is that the latter is composed of densely-packed multi-face equiaxial AlN grains,while the former is composed of loose packed β-Si3N4 column grains and a lot of second phase pockets.