A method for forming a 3D memory device is disclosed. A gate electrode having an inverted “T” shape is formed above a substrate. A continuous blocking layer is formed on the gate electrode. A continuous charge trapping layer is formed on the blocking layer. A first thickness of a first part of the charge trapping layer extending laterally is greater than a second thickness of a second part of the charge trapping layer extending vertically. The second part of the charge trapping layer extending vertically is removed to form a plurality of discrete charge trapping layers disposed at different levels on the blocking layer from the first part of the charge trapping layer extending laterally. A continuous tunneling layer is formed on the discrete charge trapping layers. A continuous channel layer is formed on the tunneling layer.