Bright, ambipolar, light-emitting polymer field-effect transistors in a bottom-contact/top-gate structure using poly (9,9-di-n-octylfluorene-altbenzothiadiazole) (F8BT) as a green-emitting semiconductor show balanced hole and electron mobilities, depending on the polymer dielectric. The emission zone, observed as a bright fine in the figure, is well defined and can be moved through the channel.