InGaN/GaN multiquantum well (MQW) p-n junction photodiodes with semi-transparent Ni/Au electrodes were fabricated and characterized. It was found that the fabricated InGaN/GaN p-n junction photodiodes exhibit a 20 V break down voltage and a photocurrent to dark current contrast ratio of similar to10(5) when a 0.4 V reverse bias was applied. The peak responsivity at 380 nm was 1.28 and 1.76 A/W with a 0.1 and 3 V applied reverse bias, respectively. Furthermore, a gain was found from our InGaN/GaN MQW p-n junction photodiodes possibly due to the long-lifetime of GaN based materials. Also, it was found that the low frequency noise of our photodiodes was dominated by the 1/f type noise. It was also found that the detector responsivity was around 1.76 A/W when the detector was biased at -3 V and the incident light wavelength 380 nm. For a given bandwidth of 500 Hz, the corresponding noise equivalent power and normalized detectivity D* were found to be 6.34 x 10(-13) W and 4.45 x 10(11) cm Hz(0.5)W(-1), respectively. (C) 2002 Elsevier Science Ltd. All rights reserved.