We have developed a kinetic model for arsine decomposition on GaAs(001) that accounts for the effect of the surface reconstructions on the rates of As4 and As2 desorption. The main assumption of the model is that As2 desorbs more slowly from Ga sites than from As sites. The model accurately simulates the temperature-programmed desorption of arsenic from GaAs(001). In addition, it reveals how the As coverage and the As2 and As4 production rates depend on the conditions employed during GaAs metalorganic vapor-phase epitaxy.