A split-gate type nonvolatile memory device includes a semiconductor substrate having a first conductivity type, a deep well having a second conductivity type in the semiconductor substrate, a pocket well having the first conductivity type in the deep well, a source line region having the second conductivity type in the pocket well, an erase gate on the source line region, and a first floating gate and a first control gate stacked sequentially on the pocket well on a side of the erase gate. The pocket well is electrically isolated from the substrate by the deep well, so that a negative voltage applied to the pocket well may not adversely affect operation of other devices formed on the substrate.