The use of a tirmethylindium-trimethylarsenic adduct, which is synthesised in the gas phase, as the In source, and AsH3 as the primary As source is reported for the growth of high-quality Ga1−xInxAs (x<0.20). The improved epitaxial layers have higher mobilities and lower background doping than those grown with trimethylarsenic as the sole As source. The effects of elevated growth temperatures are also reported.