Field-emission currents from SiO2- or MgO-coated carbon nanotube (CNT) emitters are larger than for uncoated equivalents. Moreover the coated emitters exhibit lower turn-on fields and it is shown that the MgO or SiO2 films protect the CNT tips during field emission, which improves the lifetime stability of these emitters. The Figure shows an SEM image of a SiO2-coated CNTemitter.