Silicon nitride compacts doped with Al2O3 and Y2O3 were sintered by microwave heating in a multimode cylindrical cavity applicator operating at 2.45 GHz. The densification and the alpha-->beta phase transformation behavior of the microwave-sintered silicon nitride were investigated and compared with those of conventionally sintered materials. Microwave heating enhanced the densification and the alpha-->beta phase transformation. The silicon nitride containing 12 wt% additives showed more enhanced densification and alpha-->beta phase transformation than that containing 8 wt% additives. (C) 1997 Elsevier Science Limited.