The present disclosure provides a semiconductor memory device and a method for manufacturing the semiconductor memory device. The method includes steps of: providing a substrate including a storage area and a peripheral area, wherein the storage area has a contact plug, a bit line structure adjacent to the contact plug, an air gap between the bit line structure and the contact plug, a barrier layer conformally overlaying the bit line structure, and a landing pad above the barrier layer; forming a trench between the storage area and the peripheral area; filling the trench with a nitride material; forming a first oxide layer above the nitride material in the trench and on the landing pad; forming a nitride layer above the first oxide layer; and forming a second oxide layer above the nitride layer.