Abstract Gallium interactions with silicon (100) are studied with Auger electron spectroscopy and LEED to correlate the desorption energies with surface coverages and structures in isothermal desorption experiments. Some evidence for a temperature-induced change from a Stranski-Karstanov to a Volmer-Weber growth mode between 600 and 700 K is presented. In the temperature range 800–900 K, three different kinetic regimes are observed. Between 0 and 0.5 monolayers (ML), first-order desorption is observed from a well-ordered Ga overlayer (Si : Ga 2 × 2), with a desorption energy of 2.9 ± 0.2 eV and a pre-exponential factor of 3 × 10 16 ± 1 s −1 Between 0.5 and 1 ML, first-order desorption is also observed from a well-ordered Ga layer (Si : Ga 8 × 1), but the desorption energy decreases to 2.3 ± 0.2 eV with a pre-exponential factor of to 8 × 10 12 ± 1.2 s −1. Above 1 ML, zeroth-order desorption from Ga islands on top of an ordered Ga monolayer is observed, and the desorption energy of the combination of surface species is 2.61 ± 0.07 eV with a pre-exponential factor equal to (4±3) × 10 13 ML s −1. It is suggested that atoms from the islands and the ordered layer are kinetically coupled, and that the islands cover too little of the surface to exhibit the bulk heat of vaporization of liquid Ga, 2.9 eV. The observed kinetic regimes are correlated with the surface structures proposed in the preceding paper.