 This results in an energy barrier between the drain and the source, raising the threshold voltage Vt (the gate-source voltage necessary for current to flow through the transistor).The electrons can be removed again by applying a negative bias on the control gate.A SONOS memory array is constructed by fabricating a grid of SONOS transistors which are connected by horizontal and vertical control lines (wordlines and bitlines) to peripheral circuitry such as address decoders and sense amplifiers.