Abstract: Using the GaN epilayer which was grown on Si(111) by MOCVD to fabricate GaN ultraviolet detectors is reported in this paper. The detectors exhibit a high and flat responsivity in UV region with the wavelength from 250nm to 360nm and a sharp cut-off at 363nm. At 357nm, a maximum responsivity of 6.9A/W is achieved under 5V bias. The relationship between the responsivity and the bias voltage shows that the responsivity saturates when the bias voltage reaches 5V.