A semiconductor apparatus includes a channel layer, a barrier layer, a source contact and a drain contact, a first doped group III-V semiconductor, a group III-V semiconductor, and a second doped group III-V semiconductor. The barrier layer is disposed on the channel layer. The source contact and the drain contact are disposed on the channel layer. The first doped group III-V semiconductor is disposed on the barrier layer. The group III-V semiconductor is disposed on the first doped group III-V semiconductor and between the source contact and the drain contact. The second doped group III-V semiconductor is disposed on the group III-V semiconductor and between the source contact and the drain contact. The group III-V semiconductor has a central region covered by the second doped group III-V semiconductor and a peripheral region free from coverage by the second doped group III-V semiconductor.