In this work, a semi-insulating GaN film is obtained in the Al+ implanted (by energy and dose: 500 keV and 10(14)-10(15) cm(-2), respectively) area. Measurements of double crystal X-ray diffraction (XRD) rocking curve shows that the implanted samples still remain a good quality of crystallinity. This may identify that the vanishment of the band edge emission with phonon replicas is due to the ion implantation-induced deep traps located in the forbidden gap, but not due to the change of the crystal structure. In order to detect the position of the traps, we developed a new method, namely photo-stimulated current spectroscopy (PSCS) in our measurement. Three two-component deep traps located at 1.77 eV (with 1.90 and 1.77 eV components), 1.17 eV (1.24 and 1.16 eV components) and 0.88 eV (0.90 and 0.86 eV components) below the conduction band minimum were found in the annealed sample. The two components may be due to the different levels in one trap. It is expected that the PSCS is suitable for measuring the deep levels in all semi-insulating semiconductor films.