A superplastic beta -SiAlON was used as an interlayer to diffusionally bond a hot-pressed silicon nitride to itself, The bonding was conducted in a graphite furnace under a constant uniaxial load of 5 MPa at temperatures varying from 1500 degrees to 1650 degreesC for 2 h, followed by annealing at temperatures in the range of 1600 degrees to 1750 degreesC for 2 h, The bonds were evaluated using the four-point-bend method at both room temperature and high temperatures. The results indicate that strong, void-free joints can be produced with the superplastic beta -SiAlON interlayer, with bond strengths ranging from 438 to 682 MPa, and that the Si3N4 joints are heat resistant, being able to retain their strength up to 1000 degreesC (635 MPa), and therefore have potential for high-temperature applications.