The governing equation and boundary conditions for the heat-diffusion problem associated with Ar+-laser irradiation of semiconductors are examined. Expressions are derived which, along with a numerical procedure developed here, enable us to compute scanning-Ar+-laser-induced temperature rise efficiently. Computations are carried out to obtain surface temperature changes on GaAs substrates resulting from irradiation of the scanning Ar+ laser in an experiment setup reported in the literature for laser-assisted chemical beam epitaxy. Comparisons are made between measured and computed temperature rise. Sensitivity tests are performed to assess the effects of scanning frequencies and setting of location of the substrate thermal contact on the computed temperature rise. Implications of transient temperature rise for investigations on the mechanisms responsible for Ar+-laser-induced growth modifications are discussed.