The adsorption and thermal desorption of chlorine on GaAs(100) surfaces prepared either As‐rich or Ga‐rich has been studied using Auger electron spectroscopy, thermal desorption spectroscopy (TDS), and low‐energy electron diffraction (LEED). The initial adsorption occurs more rapidly on the Ga‐rich surfaces, however saturation coverages appear equal on both As‐ and Ga‐rich surfaces. Monitoring the As and Ga Auger signals during adsorption reveals a consistent drop in the As signal while the Ga signal remains constant, which may be a result of a replacement reaction between Cl and As. Sputter damaged surfaces result in more exposed Ga, and hence, 20% more chlorine can be adsorbed onto this surface. LEED and TDS experiments on clean surfaces reveal that desorption of As2closely follows observed reconstruction changes. Chlorine saturated surfaces, however, show no noticeable reconstruction change from that of the clean surface, and upon heating the saturated surface, only GaCl and As2are seen as desorption products. Both the adsorption and desorption behavior of chlorine suggest a preferential formation of a Ga–Cl bond at the GaAs surface.