A submount substrate for mounting a light emitting device and a method of fabricating the same, wherein since a submount substrate for mouthing a light emitting device in which a Zener diode device is integrated can be fabricated by means of a silicon bulk micromachining process without using a diffusion mask, some steps of processes related to the diffusion mask can be eliminated to reduce the manufacturing costs, and wherein since a light emitting device can be flip-chip bonded directly to a submount substrate for a light emitting device in which a Zener diode device is integrated, a process of packaging the light emitting device and the voltage regulator device can be simplified.