Dual implants of C+and Ga+ions in GaAs have been investigated by sheet‐resistivity and Hall‐effect measurements. Efficient doping has been achieved by dual implantation, even at an annealing temperature of 700 °C. Analysis of electrical profiles indicates that the concentration of substitutional atoms in As sites is less than the implanted dose; the remaining C atoms are believed to out‐diffuse through encapsulation during annealing. Although the doping efficiency for the dual implants is higher than that of the single implants, the effective compensation ratio is about the same, which suggests that ’’self‐compensation’’ may be the predominant mechanism in the implanted samples.