The spark plasma sintering (SPS) of B6O ceramics using a highly crystalline boron suboxide powder with a low oxygen deficiency level is reported. The monolithic boron suboxide ceramic exhibited a room-temperature strength of 300 +/- 20 MPa, which is comparable to the strength of monolithic boron carbide. With increasing flexural test temperature, the strength of the boron suboxide ceramics increased to 450 MPa at 1400 degrees C. The increase in strength with the temperature is associated with the unique microstructure of boron suboxide grains, which allows intergranular "brittle" fracture along subgrains even at 1400 degrees C. This suggests that even higher strengths can be achieved.