Experiments show that silicon at 100 K can be etched by 1 keV electrons, when simultaneously exposed to a beam of thermal (300 K) SF 6. A yield has been found of approximately 0.4 Si atoms per incoming electron. The etch mechanism has been investigated by mass spectrometry and time-of-flight measurements of the ejected species. The results indicate that during etching SiF 4 is formed, which subsequently evaporates. In addition, species are sputtered from the target with relatively high energies. Mechanisms for the formation of these energetic particles are discussed.