A sintered silicon carbide matrix component for a semi-conductor diffusion furnace results from sintering a mixture of three types of silicon carbide powder. The mixture includes fine silicon carbide having an average particle size of 0.1-10 microns, intermediate silicon carbide having an average particle size of 12-30 microns and coarse silicon carbide having an average particle size of 40-200 microns. The difference between the average particle sizes of the three types of powder is at least 10 microns.