High-temperature tensile deformation behavior of high-purity HIPed silicon nitride material was investigated in the temperature range between 1600 degreesC and 1750 degreesC. Recoverable anelastic and non-recoverable deformation was observed in high-purity HIPed silicon nitride. A power-law deformation model analogous to rheological models was used to distinguish the different deformation components. A stress exponent n = 1.64 and an activation energy Q(1) = 708 kJ/mol was determined for the non-recoverable deformation. For the anelastic deformation a stress exponent p = 4 and an activation energy Q(3) = 619 kJ/mol was observed. Diffusional creep and grain boundary sliding with the accomodation process responsible for the anelastic component are discussed as deformation mechanisms.