Minority- and majority-carrier traps were studied in GaN pn junctions grown homoepitaxially by MOCVD on n+ GaN substrates. Two majority-carrier traps (MA1,MA2) and three minority-carrier traps (MI1, MI2, MI3) were detected by deep-level transient spectroscopy. MA1 and MA2 are electron traps commonly observed in n GaN on n+ GaN and sapphire substrates. No dislocation-related traps were observed in n GaN on n+ GaN. Among five traps in GaN pn on GaN, MI3 is the main trap with the concentration of 2.5x1015 cm-3.