AlxN1−xfilms were prepared on GaAs(110) surfaces at room temperature by simultaneous evaporation of aluminum and exposure to a beam of ammonia molecules (reactive molecular‐beam epitaxy). The formation of aluminum nitride was followed by using photoemission spectroscopy excited with ZrM&zgr; radiation (h&ngr;=151.2 eV). The composition of the deposited films was monitored by recording the N(1s) and Al(2p) core lines excited with MgK&agr; radiation (h&ngr;=1253.6 eV). The intensity ratio of these core levels as a function of impinging rate ratioz=&ngr;(NH3)/&ngr;(Al) was compared with the intensity ratio determined with an AlN standard under the same experimental conditions. Aluminum nitride was found to form at room temperature forzvalues larger than some 104.