Abstract Nanoscale order caused by self-assembling of 1B4Sb and 4B10Sb clusters in GaAs:(B, Sb) is described. Self-assembling occurs in wide ranges of temperature and impurity concentration. Co-doping with boron and Sb isoelectronic impurities transforms GaAs into GaAs-rich B x Ga 1− x Sb y As 1− y quaternary alloy. The self-assembling conditions are obtained from 0 to 800 °C with boron and Sb concentrations from x=1×10 –5 to x=2×10 –4 and from y=5×10 –4 to y=0.01, respectively. If Sb content is much larger than that of boron almost all boron atoms are in 1B4Sb clusters up to 800 °C and other boron impurities are isolated. If boron content is nearly equal or larger than that of Sb the formation of 4B10Sb clusters is preferential.