Codoping of p-type GaN with Mg and Si was investigated to determine its effect on deep level luminescence. By codoping with Si, the absolute intensity of the 2.8-eV blue luminescence band, previously tentatively attributed to deep donor-acceptor-pair (DAP) emission, decreased by more than an order of magnitude. The observed decrease is attributed to the reduction of the concentration of deep donor nitrogen vacancy complexes. The dependence of the emission peak position on hole concentration was investigated. A blueshift was observed with increasing carrier concentration. The shift of the blue band with carrier concentration and excitation intensity is explained semiquantitatively by a potential fluctuation model indicating its importance in DAP recombination.