  Based on ab initio calculations of Ga_{1-x}Mn_xN_yAs_{1-y} and
Ga_{1-x}Mn_xC_yAs_{1-y}, we propose a new codoping method to enhance the Curie
temperature T_c of diluted magnetic semiconductors. The solubility of Mn can be
increased up to high concentration by the codoping of N or C to reduce the
lattice and volume expansion caused by Mn doping. It is found that the impurity
band of the majority spin is strongly broadened and pushed up into the higher
energy region due to the strong p-d hybridization caused by the codoping, and
the T_c becomes higher than the room temperature at x>0.06.
