PURPOSE: To obtain a jig or tool for semiconductors, having a high purity, little in staining from environments, enabling to easily remove impurities with an acid, etc., and free from the staining of semiconductor elements, etc., in the thermal treatment processes of the semiconductors, etc., by specifying the diameters of voids existing on the surface.

CONSTITUTION: Silicon carbide powder having particle diameters of 0.5-10μm, an average particle diameter of 1.5-6μm, and a metal impurity concentration of ≤1ppm is mixed with 0-20wt.% of carbon powder having particle diameters of 0.1-4μm, and with a binder, molded, calcined at 500-1000°C, and subsequently sintered at 1600-2000°C for 30min to 20hr in an inert gas atmosphere or under vacuum. The obtained porous silicon carbide molded product is thermally treated in an atmosphere comprising HCl gas or Cl gas, and the thus purified product is impregnated with molten highly pure silicon (≥10) at 1450-1700°C to obtain the sintered product comprising 60-90wt.5 of the silicon carbide and 10-40wt.% of silicon. E.g. silicon wafers are longitudinally arranged to obtain a wafer boat 11 comprising columnar members 11a, 11b, 11c and plate-like members 11d, 11e and having ≤10μm diameter voids on the surfaces.