alpha-SiAlON/alpha-SiC composites with 0-40 wt% alpha-SiC were synthesized by spark plasma sintering for 5 min at 1800 degrees C under 20 MPa pressure. A self-reinforcing microstructure with both elongated alpha-SiAlON and alpha-SiC grains, was formed. Flexural strength and fracture toughness were significantly improved due to the in situ reinforcement. High fracture toughness up to 8.2 MPa center dot m1/2 was obtained in the 40 wt% SiC composition.