The surface reactions and kinetic phenomena of GaAs mono-molecular layer growth by using chemical adsorption of Ga(CH3)(3) (trimethylgallium (TMG)) and arsine (AsH3) were investigated. The monolayer growth on GaAs(100) was investigated as a parameter of injection duration, injection pressure, and evacuation duration of TMG and AsH3 in an ultra-high vacuum system to confirm the monolayer growth of the GaAs film. It has been found that the growth rate per cycle was strongly influenced by the surface stoichiometry of arsenic during growth. The characteristic growth mode which is not only an exact monolayer growth but may also be below and over monolayer growth is discussed. Subsequently, in-situ analysis of monolayer growth by using mass spectrometry during monolayer growth is presented. As a result, it has been concluded that the adsorption species might be GaCH3 under monolayer growth conditions. The model of the surface reaction in monolayer growth was deduced and discussed.