Thin films comprising semiconductor nanocrystals are emerging for applications in electronic and optoelectronic devices including light emitting diodes and solar cells. Achieving high charge carrier mobility in these films requires the identification and elimination of electronic traps on the nanocrystal surfaces. Herein, we show that in films comprising ZnO nanocrystals, an electron acceptor trap related to the presence of OH on the surface limits the conductivity. ZnO nanocrystal films were synthesized using a nonthermal plasma from diethyl zinc and oxygen and deposited by inertial impaction onto a variety of substrates. Surprisingly, coating the ZnO nanocrystals with a few nanometres of Al2O3 using atomic layer deposition decreased the film resistivity by seven orders of magnitude to values as low as 0.12 Ω cm. Electron mobility as high as 3 cm(2) V(-1) s(-1) was observed in films comprising annealed ZnO nanocrystals coated with Al2O3.