Vertical polymer hot-carrier transistor using the low bandgap material poly(3-hexylthiophene) as both the emitter and the collector are studied. The common emitter current gain is shown to depend on the LiF thickness and the emitter thickness, with maximal value at 31. Current density as high as 31 mA cm2 is achieved when collector voltage is -10 V. For the device using blend of poly(3-hexylthiophene) and high bandgap polymer poly(9-vinylcarbazole) as the emitter, the current density rises sharply to 428 mA cm2. The brightness of 3000 cd m2 is obtained as a polymer light-emitting diode is driven by the transistor with the same area. The transistor can be operated at 100 kHz.