UV metal-semiconductor-metal (MSM) photodetectors (PDs) based on the AlGaN/GaN high-electron-mobility transistor (HEMT) structure with the low-temperature (LT) AlGaN intermediate layer atop were fabricated. A much lower dark current subsequently obtained was in fact benefited by the insertion of the LT AlGaN intermediate layer. In addition, the foregoing structure also rendered PDs with better gate controllability. For the MSM PD structure grown on the LT AlGaN intermediate layer, the resultant responsivity at 360 nm varied from 0.11 to 0.12 A/W when the device was biased from 2 to 5 V while the UV/visible rejection was estimated to be around 10(3). With a 5 V applied bias, the corresponding noise equivalent power and normalized detectivity (D-*) determined were 2.65x10(-10) W and 1.74x10(9) cm Hz(0.5) W-1, respectively. (c) 2008 The Electrochemical Society. [DOI: 10.1149/1.2988129] All rights reserved.