In this study, we fabricated Aluminum Nitride （AlN） ceramics containing AlN whiskers grown by direct nitridation of Al-Si binary melt. We evaluated their microstructures and thermal conductivities. The samples containing 4 vol％ of the AlN whiskers were fully densified at 1650℃ for 10 min using spark plasma sintering （SPS） and Y2O3-CaO-B sintering additives. The microstructures were almost isotropic. This means the whiskers do not work as a seed crystal for the formation of the columnar microstructures, but a sintering additive for promoting the densification at the initial stage of sintering. Si impurity contained in the whiskers is suggested to work as a part of the sintering additives. The thermal conductivity of the sample containing whiskers was around 80 W･m-1･K-1, which is comparable to that of the sample not containing whiskers.
