A new fabrication technology of polycrystalline diamond-clad Si microtips using microwave plasma chemical vapor deposition (MPCVD) has been developed to improve the characteristics of electron field emission from the pure Si tips. A uniform and smooth coating morphology for the diamond-clad Si tips have been achieved. Electron emission currents of diamond-clad tips are much higher than those of pure Si tips. Such great improvement is attributed to the lowering of the effective work function in the diamond-clad tips. The effects of phosphorus- and boron-doped diamond-clad Si tips have been also studied in comparison with the undoped ones. The current-voltage characteristics of the undoped diamond-clad tips were further enhanced by the in-situ doping of phosphorus or boron due to a higher electron supplement. Moreover, the P-doped diamond-clad tips show a better field emission performance as compared to the B-doped ones. This difference is surmised to be associated with the higher electron conductivity and defect densities of P-doped diamond films.