AlN, an important semiconductor with the widest band gap among III-nitrides, was employed to construct solar blind metal–semiconductor–metal photodetectors (MSM-PDs). MSM-PDs were fabricated on AlN epitaxial thin films deposited on GaN/sapphire using a helicon sputtering system at a low temperature of 300 °C. The dark current of the device is as low as 200 fA at 20 V and the photocurrent illuminated by a D2 lamp increases more than two orders of magnitude. The photocurrent increases almost linearly with the incident optical power at the wavelength of 200 nm. The results show that the low temperature grown AlN MSM device is suitable for the application of deep UV detection.