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Abstract: The external quantum efficiency in the spectral wavelength range 5–500nm of a large active area Pt/n-type GaN Schottky photodiode that exhibits low reverse bias leakage current, is reported. The Schottky photodiodes were fabricated from n-/n+ epitaxial layers grown by low pressure metalorganic vapour phase epitaxy on single crystal c-plane sapphire. The current–voltage () characteristics of several 0.25cm2 devices are presented together with the capacitance–voltage () characteristics of one of these devices. A leakage current as low as 14 pA at 0.5V reverse bias is reported, for a 0.25cm2 diode. The ultraviolet quantum efficiency measurements show that the diodes can be used as radiation hard detectors for the 5–365nm spectral range without the use of visible blocking filters. A peak responsivity of 77.5mA/W at 320nm is reported for one of the fabricated devices, corresponding to a spectral detectivity, . The average detectivity between 250 and 350nm, for the same device, is reported to be . The spatial responsivity uniformity variation was established, using H2 Lyman-α radiation, to be ±3% across the surface of a typical 0.25cm2 diode. [Copyright &y& Elsevier]