Surface migration lengths of As adatoms on (4 1 1)A GaAs surfaces during molecular beam epitaxy were determined for the first time from lateral profiles of the arsenic content (x) in the GaAsxP1-x layers grown on GaAs channeled substrates (CSs) using As-4 and P-2 beams. The x on the (4 1 1)A side-slope region near the edge of the (1 0 0) region increased from that on the flat (4 1 1)A GaAs substrate, indicating that As adatoms flow from the (1 0 0) region to the (4 1 1)A side-slope region. The observed surface migration length of As adatoms was 15 +/-2 mum on the (4 1 1)A GaAs surface at 535 degreesC. The surface migration length of As adatoms on (4 1 1)A GaAs surface slightly increases to 20 +/-2 mum with increase of the substrate temperature to 605 degreesC. The substrate temperature (T-s) dependence of surface migration length of As adatoms on the (4 1 1)A GaAs surface is discussed.