We fabricated AlN ceramics at sintering temperatures with a minimum of 1450 degrees C using spark plasma sintering (SPS) with Y2O3-CaO-B or Y2O3-CaO-LaB6 sintering additives. The relative densities of the AlN ceramics sintered at 1500 degrees C for 10 min with a uniaxial pressure of 50 MPa exceeded 98%, indicating sufficient densification. However, with decreasing the sintering temperature to 1450 degrees C, the relative densities were decreased to similar to 90%. An increase in the uniaxial pressure to 100 MPa or the extension of sintering time to 30 min were found to promote the densification of AlN ceramics. The relative densities of the AlN ceramics sintered reached 99% even at a sintering temperature of 1450 degrees C. The samples had dense and fine textures with an average grain size of similar to 1 mu m. The thermal conductivities of the samples varied with relative density between 30 and 80 W m(-1) K-1. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.