A nonvolatile memory device includes a semiconductor well region of first conductivity type on a semiconductor substrate and a common source diffusion region of second conductivity type extending in the semiconductor well region and forming a P-N rectifying junction therewith. A byte-erasable EEPROM memory array is provided in the semiconductor well region. This byte-erasable EEPROM memory array is configured to support independent erasure of first and second pluralities of EEPROM memory cells therein that are electrically connected to the common source diffusion region.