Enhanced etching of a room temperature Si(100) surface is observed during exposure to a neutral hyperthermal chlorine beam. Etching is monitored by mass spectrometric detection of silicon chloride products (SiClx) in the scattered flux. The etchant beam is produced by laser vaporization of cryogenic chlorine films; it consists of ≥93% molecular chlorine with a variable kinetic energy distribution depending on laser energy. The sustained etching rate, based on detection of SiCl3+, is independent of energy when the maximum Cl2 kinetic energy is less than 3 eV but increases by a factor of 3.6±1 when the maximum energy is ≊6 eV. No etch products are detected with thermal Cl2. The etching rate of the most energetic chlorine is greater than the thermal chlorine etching rate by a factor of ≥30.