This report describes the fabrication and characteristics of GaN p–n junction diodes on free‐standing GaN substrates with low dislocation density. We have demonstrated GaN p–n junction diodes with a unique field‐plate (FP) structure. The breakdown voltage VB is further improved due to the FP structure and the low dislocation density. The breakdown voltage of a diode of 60 µm in diameter with the FP structure is over −1000 V, and the leakage current is below 10−9 A until reaching the breakdown voltage. Even in larger diodes (100 and 200 µm in diameter) with FP, the breakdown voltage is over −800 V. However, the specific on‐resistance Ron is high due to damage by the plasma process of sputtering. The specific on‐resistance is further improved due to using a low damage passivation film. As a result, a specific on‐resistance of 1.2 mΩ · cm2 is obtained.