An oxygen induced sharpening process of field emitter tips, W[111], for use in a scanning tunneling microscope aligned field emission microcolumn system has been developed. The sharpening process which depends on processing temperature and oxygen pressure can be used to control tip radius accurately with reliability and reproducibility. The measured tungsten removal rate was approximately 13 angstrom/min at a processing temperature of congruent-to 1650 K and at an oxygen pressure of congruent-to 4 X 10(-5) Torr. The process is primarily intended for more accurate control of the tip radius and hence performance of newly etched tips, although damaged or blunt tips can also be resharpened in situ with this process. Favorable emission characteristics of the oxygen processed tips have been observed with microcolumn operation : (1) reasonably stable emission current, (2) low extraction voltage, (3) reproducible threefold symmetric emission patterns, and (4) small emission angle.