Thermal effects in molybdenum tips with and without diamond coatings are analyzed. An attempt is made to identify:; ＇intrinsic＇＇ mechanisms that might trigger catastrophic vacuum breakdown. A new theoretical treatment is employed to study the thermal response of tip emitters which takes into account the correlative effect between field emission and its resultant temperature rise at the tip. In both uncoated and chemically vapor deposited diamond coated Mo tip emission regimes, the location of the hot spot is found to be at the tip apex. It is also shown that higher emission current densities can be obtained from a coated tip before the melting temperature of Mo is reached compared to that of an uncoated tip for the same geometry and dimension.