TiB2‐particle reinforcement is one of the most successful methods for improving the fracture toughness of SiC ceramics.1–3Commercially available TiB2powders, however, have a large particle size and/or are highly reactive so that they are not favorable as a starting powder. In the present work, TiB2particles are formed by an in situ reaction between TiC and boron. The reaction takes place during sintering between 1000° and 1600°C and is accompanied by a large volume expansion. Under optimum conditions, dense composites (>98% of theoretical) can be obtained by pressureless sintering using B and C as sintering additives. The in situ reaction method enables, for the first time, a complete densification of SiC‐particulate composites by pressureless sintering. The fracture toughness of the composites was approximately 30% higher than that of the monolithic SiC