The reverse bias current-voltage (I–V) characteristics of GaN-based light-emitting diodes (LEDs) were investigated. The leakage current exhibits exponential dependence on the bias voltage with different exponents for various voltage ranges. The leakage current is closely related to the density of dislocations. The number of dislocations in GaN was determined by atomic force microscopy combined with hot H3PO4 etching. Dislocations with a screw component in the GaN films were found to have a strong influence on the reverse leakage current of LEDs. The dislocation electrical activity in GaN grown on c-plane sapphire is different from that in GaN grown on a-plane sapphire.