At room temperature, anisotropic etching of both (100) and (111) oriented single‐crystalline silicon substrates is successfully achieved, using a thermally excited ClF3molecular beam. The morphology of the etched surface is better than that using Cl2. The etching rate is more than 50 Å/min, and the ratio of etching rate of vertical direction to that of horizontal direction is more than eight. Process‐induced damage in the metal–oxide semiconductor device was not observed from the capacitance–voltage characteristic measurements.