In order to obtain the prebreakdown and breakdown data of plain vacuum gaps in the micrometric regime relevant to field emission displays, an automatic experimental system was developed. The dc breakdown characteristics of the gap in the micrometric regime, varying from 25 to 1000 mu m, were extensively studied. The experimental results show that the highly finished broad-area metal electrodes withstand fairly high fields in relatively poor vacuum. The dc breakdown strength of a 50 mu m gap was more than 220 V/mu m at a pressure of 10(-5) Torr, while for a 1000 mu m gap, the breakdown strength was about 44.5 V/mu m for highly polished chrome-steel electrodes, 2 cm in diameter. The breakdown of a narrow (<200 mu m) vacuum gap resulted in rapid degradation, with the gap holding-off lower voltages after breakdown. However, a wider gap (500-1000 mu m) was found to exhibit conditioning, with the dc breakdown voltage increasing after each successive breakdown. The breakdown characteristics of ideal gaps with very smooth solid electrodes, presented in this work, will define the theoretical limits to which actual gaps can be stressed in a field emission display.