Efficient transport of both electrons and holes with high carrier densities is a requirement for obtaining light-emitting transistors from films of colloidal semiconductor nanocrystals. Such devices offer an approach to efficient electrically pumped nanocrystal lasers with tunable emission. Here, we report a low-voltage ambipolar thin-film transistor that features high carrier mobility and high induced carrier density by combining a PbSe nanocrystal film with a high-capacitance ion-gel gate dielectric layer (∼22 and ∼9 μF/cm2 for electron and hole accumulation, respectively). At operation voltages below 2.5 V, electron and hole densities higher than ∼1014 carriers/cm2 could be achieved in the PbSe nanocrystal film, which corresponds to ∼3 electrons or holes per particle. Carrier mobilities were also dependent on charge density and were as high as 0.4 and 0.02 cm2/(V s) for electrons and holes, respectively.