Liquid‐nitrogen‐temperature Hall mobilities of about 105 000 cm2/V sec have been achieved inn‐type epitaxial layers grown by molecular beam epitaxy (MBE). The Hall mobility of thep‐type epitaxial layers at 78 °K was about 8440 cm2/V sec. The net donor concentration and the net acceptor concentrations forn‐type andp‐type epitaxial layers were about 4×1014and 1×1014cm−3, respectively. The compensation ratio in then‐type epitaxial layers was about 0.4 as determined from the 78 °K electron mobility. Cr‐doped GaAs buffer layers for FET’s were grown in a substrate temperature range of 500–640 °C. Sheet resistances in excess of 109&OHgr;/ &laplac; were achieved when the substrate temperature during the growth was about 580 °C or higher. The amount of Cr that can be incorporated into the epitaxial layer showed a strong substrate temperature dependence.