The deep levels in GaN associated with yellow luminescence transitions have been investigated using photoluminescence, Hall measurements, and deep level transient spectroscopy (DLTS). Hall measurements on Si-doped GaN show the presence of donor levels at ∼18, ∼35, and ∼70 meV, which are respectively associated with the Si shallow donors, O impurities, and the nitrogen vacancies (VN). DLTS measurements, on the other hand, reveal trap levels at Ec-0.1 eV, Ec-(0.2–0.24) eV, and Ev+0.87 eV. The trap level at Ec-0.1 eV obtained from DLTS can be correlated to the 70 meV deep donor (VN) obtained from Hall measurements. The deep donor band at Ec-(0.2–0.24) eV is attributed to the ON related defect complex decorated along dislocation sites while the hole level at Ev+0.87 eV is attributed to the Ga vacancy (VGa). Thermal annealing at 750 °C in nitrogen ambient results in reduction of yellow luminescence, which could be due to decrease in the concentration of VN and ON-related defect complexes. From these observations, we propose that yellow luminescence in GaN arises from the transitions from the Ec-(0.2–0.24) eV levels to the deep level at Ev+0.87 eV. © 2004 American Institute of Physics.