We demonstrate a solution-processed colloidal quantum dot (CQDs) photodetector with the configuration of a field-effect transistor (FET), in which the drain and source electrodes are fabricated by a shadow mask. By blending PbS CQDs into the hybrid blend, poly(3-hexylthiophene) (P3HT) and 6,6-phenyl-C sub(61)-butyric acid methylester(PCBM), the photosensitive spectrum of the nanocomposite blend is extended into the near-infrared region. A FET-based photodetector ITO/PMMA (180 nm)/P3HT:PCBM:PbS (110 nm)/Al, in which PMMA (polymethylmethacrylate) acts as the dielectric layer and P3HT:PCBM:PbS (in weight ratio of 1:1:1) as the active layer, shows a broad spectral bandwidth, a responsivity of 0.391 mA W super(-1) and a specific detectivity of 1.31 x 10 super(11) Jones are obtained at V sub(GS) = 1 V under 600 nm illumination with an intensity of 30 mu W cm super(-2). Therefore, it provides an easy way to fabricate such a FET-based photodetector with a channel length of some hundreds of micrometers by a shadow mask.