The de prebreakdown and breakdown characteristics of micrometric gaps varying from 25 to 1000 mu m, between highly polished 2 cm diam spherical electrodes, were extensively investigated at similar to 10(-6) Torr. The current-voltage characteristics of the above gaps obey Fowler-Nordheim behavior, confirming that the prebreakdown conduction was dominated by high field electron tunneling. The breakdown voltage derived from the prebreakdown data took the form of a power relation of gap distance as V-b=Kd(alpha). Experimental results showed that highly polished metal electrodes can withstand very high fields in relatively poor vacuum : 220 V/mu m for a 50 mu m gap, 130 V/mu m for a 300 mu m gap. The breakdown of a narrow (less than or equal to 200 mu m) gap resulted in rapid degradation, causing damage to both anode and cathode, while wider gaps (400-1000 mu m) were found to exhibit spark conditioning, with the de breakdown voltage increasing after each successive breakdown, causing damage only to the anode. A de-glow-discharge treatment improved the gap insulation capability significantly and could recover the degraded gap insulation capability caused by spark discharge breakdown in small gaps. The experimental results also showed that the electrode surface roughness per se does not play a key role in influencing the breakdown characteristics after the de glow-discharge pretreatment.