The excitonic emissions near band edge, the donor-to-acceptor pair (DAP) emissions and the yellow luminescence (YL) in undoped GaN and As-doped GaN at a low doping level have been investigated. At 4.2 K, the intensity of the DAP emissions around 3.28 eV were observed to increase when the As concentration is increased. This enhancement has been correlated with an increase of the As-related isoelectronic centers. On the other hand, a remarkable reduction of the yellow luminescence due to the incorporation of As into GaN is found at 4.2 K, and it persists up to room temperature where the DAP signal has got quenched due to thermal ionization. These results suggest that the suppression of the YL is due to the passivation of the YL deep centers by the As-incorporation.