The effects of surface stoichiometry on Be doping in GaAs grown by molecular layer epitaxy have experimentally been investigated. Be-doped p +-GaAs layers were grown on (0 0 1)-oriented GaAs substrates by intermittent supply of AsH 3 and triethylgallium (TEG) in an ultra-high vacuum. Be(MeCp) 2 was used as a p-type dopant gas. The surface stoichiometry before introducing the dopant gas was controlled by changing the AsH 3 and TEG injection sequence and supply time. The doping characteristics were evaluated by secondary ion mass spectroscopy analysis. It was found that doping characteristics of Be-doped GaAs are strongly dependent on the doping sequence and surface stoichiometry. This experimental result and the Be doping mechanism are discussed on the basis of rate law of the surface chemical reaction.