Kinetics of epitaxial growth of GaAs from trimethylgallium (TMG) and arsine in organometallic chemical vapor deposition (OMCVD) have been suggested in the past to occur according to the Langmuir-Hinshelwood (L-H) or Langmuir-Rideal (L-R) mechanism [1–3], where competitive chemisorption of the Ga- and As-containing species is assumed. In contrast, formation of sp3 bonds on the GaAs growth front suggests that the Ga-containing species are less likely to chemisorb onto Assites, while the As-containing species are less likely to chemisorb onto Ga-sites. In addition, an analysis of probable chemical reactions and the unlikely event of homogeneous dissociation of hydrogen molecules indicate that the chemisorption of hydrogen must be included in the growth kinetics. Since H-As and H-Ga bonds have similar characteristics, such hydrogen chemisorption probably occurs on all sites. Thus, a mix of selective (Ga, As) and competitive (H2) chemisorption processes is likely to be present in practice. Furthermore, the presence of chemisorbed hydrogen will alter the surface As bonds, which, in the absence of hydrogen, are known to dehybridize and dimerize. These basic issues have not been addressed in existing OMCVD growth models. Therefore, an analysis of the adsorption and growth processes, in the epitaxy of (100)GaAs is presented in this paper, with particular attention to the above issues.