TiB2-SiC-C and TiB2-TiC-C heteromodulus ceramics were sintered by reactive hot pressing of TiC-B4C-Si and TiC-B4C precursors at 1830 °C and 30 MPa. Sintering time at the maximum temperature was between 2 and 8 min. The reactions in TiC-B4C-Si green body create submicron (100–400 nm) TiB2 crystals inside silicon carbide grains as well as BxSiyCz nanofibers, which nucleate near SiC surfaces. Low hardness graphite platelets are formed within the hard matrix during the in-situ exothermic reaction. “Soft-hard” grain combination produces substantially improved fracture toughness (up to 9 MPa m1/2). The materials also demonstrate high thermal conductivity (up to 120 W/m∙K) and high thermal shock resistance. The thermal shock crack growth is arrested by the graphite platelets.