A fabricating method of nitride semiconductor substrate is provided. First, a first substrate including a first base material, a nitride semiconductor template layer stacked on the first base material, and a first dielectric layer stacked on the nitride semiconductor template layer is provided. Then, the first dielectric layer and the nitride semiconductor template layer are patterned, and a second substrate including a second base material and a second dielectric layer stacked on the second base material is provided. Next, the nitride semiconductor template layer and the first dielectric layer of the first substrate are transferred onto the second dielectric layer of the second substrate through bonding and transferring processes, and then a nitride semiconductor thick film is grown from the nitride semiconductor template layer through an epitaxy process. After that, the nitride semiconductor thick film and the second substrate are separated.