We report a study of the properties of the semiconducting polymer poly(9,9-dioctylfluorene) (PFO) as a gain medium. We demonstrate amplification of blue light via amplified spontaneous emission (ASE) measurements on optically pumped PFO planar asymmetric waveguides. We show that the ASE wavelength can be tuned over a range of 20 nm by altering the supported waveguide modes. Gain/loss measurements at the peak ASE wavelength (466 nm) show that the waveguides can exhibit a large net gain of up to 74 cm-1 and have a very low loss coefficient ∼3 cm-1. These characteristics make PFO attractive as a high gain medium for short-wavelength lasers and optical amplifiers. © 2002 American Institute of Physics.