A memory device with composite contact plug and method for manufacturing the same. The composite contact plug comprises a first insulating layer deposited on a semiconductor substrate. A contact hole is formed to penetrate through the first insulation layer. A barrier layer is deposited in the contact hole and fills a portion of the contact hole. A contact plug is formed on the barrier layer and fills the contact hole. The first insulating layer is etched back until the surface of the first insulating layer is below the contact plug. A diffusion barrier layer is then deposited on the first insulating layer and the contact plug. The diffusion barrier layer is planarized until the contact plug is exposed to form a composite contact plug. The memory device is constructed on the composite contact plug.