In this paper, we present a novel blue-sensitive Si photodetector. The detector is realized as a Si diode with a vertical PN junction in the silicon-on-insulator (SOI) thin film for normal incident light. Due to the thin SOI device layer, the photodetector shows a blue-shift spectral response with the peak external quantum efficiency (QE) of 69.6% at wavelength of 480 nm. The photodetector adopts a thin layer of SiO2 as an antireflection coating and as a blocking layer for shallow ion implantation doping. The isolation trench etched through the SOI thin film to the buried oxide (BOX) provides fully electrical isolation. The device structure is simple and its performance is very high, therefore, iris in favor of monolithically integration with other micro/nanodevices. (C) 2010 Elsevier Ltd. All rights reserved.