We have investigated carbon (C) and silicon (Si) doping characteristics in GaAs and AlAs grown on (3 1 1)A and (3 1 1)B-oriented GaAs substrates by metalorganic chemical vapor deposition (MOCVD) and compared them to those on (1 0 0)-oriented substrates. For C doping in both GaAs and AlAs with CBr 4, the order of the hole concentration is (3 1 1)A ⩾ (1 0 0) > (3 1 1)B at V III < 60 . Hole concentration decreases with increasing V III ratio for all the cases. It decreases with increasing growth temperature except for AlAs on (3 1 1)B, in which case it increases with increasing growth temperature. For AlAs on (3 1 1)B, surface morphology is improved by increasing growth temperature, decreasing V III ratio and increasing CBr 4 flow rate due to the enhancement of the two-dimensional growth mode. For GaAs on (3 1 1)B, disk-like structures appear at T g = 750°C and V III = 15 . For Si doping in both GaAs and AlAs with SiH 4, the order of electron concentration is (3 1 1)B > (1 0 0) > (3 1 1)A. Electron concentration in AlAs on (3 1 1)B is about one order of magnitude higher than that on (1 0 0), while the Si-doped AlAs on (3 1 1)A exhibits p-type conductivity. For both dopants, AlAs shows apparent dependence compared with GaAs because of its reactivity but the tendencies are almost same as GaAs.