We measured the field emission (FE) properties and life time stability of single walled carbon nanotubes (SWNTs) after coating with wide-band-gap material (WBGM) and successive negative electron affinity (NEA) material, i.e., magnesium oxide and successive gallium arsenide. Their turn-on field and emission current densities were measured and compared with pristine SWNT film. The FE was increased successively after MgO coating and subsequent GaAs coating for SWNTs. A lifetime test revealed that GaAs/MgO/SWNTs protects SWNT film during FE under exposure to O2 gas. The field-enhancement factor, β, was calculated from the Fowler-Nordheim equation of FE results.