Epitaxial layers of GaAs with peak mobilities as high as 200 000 cm2/V s at 50 K have been grown in an atmospheric pressure organometallic vapor phase epitaxy reactor using trimethylgallium (TMG) and arsine. The growth conditions which lead to high‐mobility GaAs are described in this letter. Low‐temperature photoluminescence and temperature‐dependent Hall measurements are used to study the dependence of the incorporation of residual impurities on the growth temperature and arsine partial pressure. Carbon acceptor densities <1014cm−3were measured in the highest purity samples.