By embedding Ge self-assembled quantum dots (QDs) inmicrodisk cavity, resonant-cavity-enhanced waveguide photodetector (PD) with ultra-low dark current and high responsivity is experimentally demonstrated around 1.55 mu m wavelength. Ge QDs are grown on silicon-on-insulator substrate by solid-source molecular beam epitaxy. Microdisk is used to enhance the absorption efficiency of Ge QDs, and a vertical PIN diode is integrated with the microdisk to extract photo-generated current. The dark current density of our PD is as low as 0.97 mA/cm2 under - 10 V bias. At resonant wavelength of 1541.15 nm, enhanced peak responsivity of 2.13 mA/ W is obtained. The wavelength selectivity of the microdisk PD also makes it preferable for wavelength-division multiplexing optical receiver. (C) 2013 Elsevier B. V. All rights reserved.