The effects of the gate dielectrics on ambipolar transport in top-gate-type polymer light-emitting transistors with single-layer and bilayer gate dielectrics are investigated. Hole field-effect mobility is dependent on the dielectric constant of the gate dielectric onto the active layer. Hole transport of devices is affected by the dipolar disorder in the first gate dielectric layer on the active layer. Electron threshold voltage tends to decrease with increasing the total stacked gate capacitance.