Polymer light-emitting transistor is realized by vertically stacking a top-emitting polymer light-emitting diode on a polymer space-charge-limited transistor. The transistor modulates the current flow of the light-emitting diode by the metal-grid base voltage. The active semiconductor of the transistor is poly(3-hexylthiophene). Yellow poly(para-phenylene vinylene) derivative is used as the yellow emitting material. As the cathode is fixed at -12 V and the grid base voltage varies from 0.9 to -0.9 V the light emission is turned on and off with on luminance up to 1208 cd/m2. The current efficiency of the light-emitting transistor is 10 cd/A.