High-strength joining of Si3N4 ceramics has been achieved by developing a process that effectively eliminates the seam, and may allow for fabrication of large or complex silicon nitride bodies. This approach to joining is based on the concept that when sintering aids are effective in bonding individual grains, they could be equally effective in joining bulk pieces of Si3N4, Optimization of the process led to Si3N4/Si3N4 joints with room-temperature bend strengths as high as 950 MPa, corresponding to more than 90% of the bulk strength of the Si3N4, At elevated temperatures of 1000 degrees and 1200 degreesC joint strengths of 666 and 330 MPa, respectively, were obtained, which are the highest values reported to date for these temperatures. These bend strengths are also more that 90% of the strength of bulk Si3N4 measured at these temperatures.