The sticking coefficient γ of ground‐state Cl (Cl ²P 3/2 ) and spin–orbit excited Cl* (Cl ²P 1/2 ) on lightly doped n‐Si(100) was measured using resonance‐enhanced multiphoton ionization of Cl and Cl* at mTorr pressure in a Knudsen cell. For Cl only an upper limit of γ≤5×10^-5 could be obtained and for Cl* γ=4.6×10^-4 was measured. These γ values are temperature independent in the range of 300–600 K and the sum corresponds to a spontaneous etch rate of 9.4 Å/min for Si(100). SiCl 2 was the principal etch product under these spontaneous etch conditions, and no SiCl 4 was found over the given temperature range.