Weak light emission caused an ionization process of gases in the micro gag of an electrostatic actuator under a high electric field can be imaged using a high sensitive CCD camera, even if the electric field strength is below the breakdown threshold. The observation of the ionization process give an information about a space charge distribution in gases. It is found that irregular instability and the inhomogeneous distribution of electric field develop micro-discharges. The micro-discharge evaporates an electrode material, results in increasing the pressure in the gap, finally grows up to the breakdown. This effect is seemed to be remarkable, especially in narrow gaps. Furthermore, the electric breakdown threshed depends on the electrode material. Silicon-to-silicon gap configuration shows a higher breakdown threshold as well as the prebreakdown threshold in comparison with silicon-to-metal gap. It suggests that /spl gamma//sub i/ effect plays an important role in this process.