Device quality GaAs was grown at substrate temperatures as low as 430 °C, by decreasing the growth rate to 0.2 &mgr;m/h and by using dimeric arsenic. Precise doping control down to 1×1016cm−3has been easily achieved and Hall mobilities of up to 66% of the best molecular beam epitaxy values have been measured. By contrast, the use of As4under the same growth conditions led to films with poor electrical and optical properties. These results add further evidence to the superiority of As2in reducing the concentration of compensation deep levels, and provide the first conclusive evidence of its significant role in the low‐temperature growth of high quality GaAs.