With the miniaturization of MEMS (micro electromechanical systems) devices, the insulation width and the separation between electrodes in such devices have been accordingly reduced. Consequently, electrical breakdown phenomenon across micrometer-scale gap is of great practical interest for insulation designing of miniaturized devices. In this paper, breakdown and pre-breakdown phenomenon under impulse voltage application across micro-meter scale gaps fabricated on SO wafers were observed. Prior to the breakdown, it is observed that current pulse flows. Changing the electrode configuration and the application voltage polarity, charge quantity, current pulse waveform, and sparkover voltage are measured. The discharge process across micrometer-scale gap was investigated.