In a silicon-oxide-nitride-oxide-silicon (SONOS) memory device and a method of manufacturing the same, a SONOS memory device includes a semiconductor substrate, an insulating layer deposited on the semiconductor substrate, an active layer formed on a predetermined region of the insulating layer and divided into a source region, a drain region, and a channel region, a first side gate stack formed at a first side of the channel region, and a second side gate stack formed at a second side of the channel region opposite the first side of the channel region. In the SONOS memory device, at least two bits of data may be stored in each SONOS memory device, thereby allowing the integration density of the semiconductor memory device to be increased without increasing an area thereof.