Ar+ ions of 0.5 to 2 keV from a broad‐beam Kaufman ion source have been used to induce chemical etching of Si by SF6 effusing from a gas dispensing ring placed near the Si surface. Etch rates have been measured as a function of sample temperature, SF6 flux, and ion energy. As the Si temperature is reduced below 120 K the Si yield per Ar+ ion rises to reach a maximum enhancement of about 8–10 just below 100 K, compared to pure physical sputtering. The results suggest that the dominant effect of the sample temperature is to control the fluorine supply via the evaporation rate of physisorbed SF6 molecules. This etching process has been applied to produce micron‐sized, blazed gratings in Si, using Al as a hard mask. Blaze angles up to 70° have been produced by tilting the sample with respect to the ion beam.