A new composite structure of carbon nanotubes (CNTs)/Si nanowires (SiNWs) arrays have been synthesized by chemical vapor deposition (CVD) within the pores of microporous alumina template. The results of scanning electron microscopy (SEM) and transmission electron microcopy (TEM) reveal that the obtained well-aligned composite structure has a core-sheath structure and the deposited material in the carbon sheath is polycrystalline silicon. Field emission from these CNTs-sheathed SiNWs exhibits significant enhancement compared to the pure SiNWs in turn-on field, total emission Current and stability. The field emission characteristics of the composite structure are analyzed based on Fowler-Nordheirn theory. The electron field emission increased with decreasing diameter of such structure. The well-aligned core-sheath structure provides an important means to fabricate emitter devices with chemically inert surface as well as with superior performance of field emission properties. (C) 2003 Elsevier Science B.V. All rights reserved.