The present invention discloses a metal oxide semiconductor (MOS) device and a method for operating an array structure comprising the same devices. The MOS device of the present invention comprises a device layer; an ion-implanted layer formed on the device layer and providing the source, the drain and the channel; and a gate structure formed on the ion-implanted layer. Via applying a bias voltage to the gate, the carrier density in the channel region is different from that in the source region or the drain region; thereby, the MOS device of the present invention can undertake programming, erasing and reading activities. The present invention can simplify the MOS device fabrication process, reduce the operating voltage, and promote the integration density of a 2-dimensional or 3-dimensional MOS device array.