Planar GaN-based p-n(-)-n(+) photodetectors were formed through Si implantation into p-GaN. When the reverse bias was below 4 V, the photodetectors showed nearly constant dark current around 20 pA. The dark current was somewhat higher as compared to the dark current observed in conventional epitaxial grown p-i-n photodiodes. Increase in dark current may be due to the incomplete damage (induced by implantation) removal. Spectral response measurements revealed that peak responsivity was around 11.4 mA/W at 360 nm for the planar p-n(-)-n(+) UV photodetectors with a reverse bias of 1 V. It was also found that visible (450 nm)-to-UV (360 nm) rejection ratio was around 700.