PURPOSE: To obtain a silicon carbide-based sintered compact having high mechanical characteristics and high heat conductivity by adding a carbon-contg. compd. and a boron-contg. compd. as sintering aids and carrying out sintering and heat treatment in a nitrogen atmosphere under a high pressure.

CONSTITUTION: A carbon-contg. compd. such as carbon black and a boroncontg. compd. such as B4C as sintering aids are added to silicon carbide powder having 0.1-2μm average particle diameter as a base by 1-4wt.% (expressed in terms of carbon) and 0.2-0.4wt.% (expressed in terms of boron), respectivity. They are mixed with a mixing means such as a ball mill, a binder is added and the mixture is molded into a desired shape by press molding or other method and sintered at 1,950-2,000°C in vacuum or in an inert atmosphere to obtain a silicon carbide-based sintered compact having ≥88% relative density and low heat conductivity. This sintered compact is heat-treated at 1,800-2,100°C in a nitrogen atmosphere under a high pressure of 1,500-2,000atm so that the weight is increased by 0.01-5% and a sintered compact having ≥100 W/m×k heat conductivity is obtd.