GaN-based PIN alpha particle detectors are studied in this article. The electrical properties of detectors have been investigated, such as current–voltage (I–V) and capacitance–voltage (C–V). The reverse current of all detectors is in nA range applied at 30 V, which is suitable for detector operation. The charge collection efficiency (CCE) is measured to be approximately 80% but the energy resolution is calculated to be about 40% mostly because the intrinsic layer is not sufficiently thick enough.