GaN is a wide-bandgap semiconductor with still unexplored capabilities for ultraviolet detection. To exploit GaN properties better for ultraviolet detection, a metal–semiconductor–metal-type photodetector structure was designed and manufactured on a $2.2\mathrm{\mu m}$ thin GaN membrane fabricated by micromachining techniques. As a result, a very low dark current ( $30\mathrm{pA}$ at $3\mathrm{V}$ ) and a maximum responsivity of $14\mathrm{mA}/\mathrm{W}$ at a wavelength of $370\mathrm{nm}$ were obtained.