A semiconductor QD fiber amplifier (SQDFA) is proposed and theoretically researched. The fiber amplifier makes use of a tapered twin SMF coupler and a PbS QD-film is coated on the surface of it. In the tapered region, QDs will be excited by the evanescent wave of a pump and produce a gain on signal. The fiber coupler is properly designed to ensure a desired power ratio of the output signal. Using a 1530-nm signal and a 980-nm pump, an optical gain of about 8 dB is achieved with a gain efficiency of 3.48dB/cm. This SQDFA has unique advantages including suppression to the amplified spontaneous emission (ASE), simple fabrication and lower insertion loss and thus has a great potential in fiber communication systems.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.