Atomically sharp tungsten tips (<20 A˚) have been grown on a silicon substrate by chemical vapor reaction of WF6with atomically sharp preformed silicon tips. Transmission electron microscope studies show that a thickness of about 50 A˚ of tungsten is optimum for complete coverage of silicon while retaining atomic sharpness at the tip. The tungsten is nearly amorphous and is porous. These tips have potential applications in vacuum microelectronics as electron emitters and can also be used as electronic and magnetic microsensors and probes.