Uniformity is one of the most important qualifications for reliable field emission devices based on carbon nanofibers (CNFs). We synthesized CNFs by thermal chemical vapor deposition at 600 °C on the glass substrate, promising practical large-area applications. A glass cap was introduced to enhance the uniformity of CNF emitters vertically grown under the guidance of micro-grooves, which provided passages for the diffusion of precursor gas to CNF growth sites. Our CNFs, vertically leveled by the glass cap with the support of the micro-grooves, and without any post-treatments, showed excellent uniformity in field emission as well as long-term stability.