GaN photoconductive detectors were fabricated on Si (111) substrates. These detectors exhibited a sharp cutoff at the wavelength of 363 nm and a high responsivity at the wavelength from 360 to 250 nm. Both ohmic contact and non-ohmic contact detectors were studied in this article. The ohmic contact detectors exhibited a higher responsivity and a wider linear increase range in voltage-dependent responsivity than the non-ohmic contact detectors. Because the contact barriers can lower the photocurrent gain, and the built-in electric field caused by the contact barriers can increase the minority drift length at high applied voltage, the voltage-dependent responsivity of non-ohmic contact detectors increased slowly at low applied voltage and saturated earlier at high applied voltage than that of ohmic contact ones. Due to the persistent photoconductivity, effects of contact barriers on time response were negligible.