We investigated the effect of coimplantation of gallium(Ga) with carbon(C) and silicon(Si) in 6H-SiC by using Rutherford backscattering spectrometry-channeling(RBS-C) and Hall effect measurement. In the case of coimplantation of Ga with C we could not find the enhancement of the activation rate of accepters in contrast with the cases of coimplantation of Al/C and B/C. In the case of coimplantation of Ga with Si we found a drastic retrenchment of the activation rate compared with the case of coimplantation of Al/Si and B/Si. We concluded that this result originated in the difference in the site preference between Al, B and Ga.