1. A non-volatile memory device integrated in a chip of semiconductor material, wherein the memory device includes at least one sector of a plurality of memory cells, each sector including a storage region of a first type of conductivity and a further storage region of a second type of conductivity, and each memory cell including a first region and a second region of the second type of conductivity being formed in the storage region for defining a storage transistor of floating gate MOS type of the first type of conductivity, a further first region and a further second region of the first type of conductivity being formed in the further storage region for defining a further storage transistor of floating gate MOS type of the second type of conductivity, and a common floating gate of the storage transistor and the further storage transistor, and wherein the memory device further includes programming means for programming each memory cell individually by programming the corresponding floating gate through the corresponding storage transistor, and erasing means for erasing each memory cell individually by erasing the corresponding floating gate through the corresponding further storage transistor.