According to an embodiment of the disclosure, with reference to FIGS. 1 to 2B, a second word line structure part 200B is a solid structure. The cross section of a first word line structure part 200A includes a concave region AC0 in the direction perpendicular to the extension direction of word line structures. That is, the groove is dug into the first word line structure part 200A in the direction perpendicular to a semiconductor substrate 10 to form groove in the first word line structure part 200A. Illustratively, the concave region AC0 may be avoidance region BR. The groove is formed in the first word line structure part 200A, so that electric charges are mainly concentrated at the bottoms of the groove, and relatively few charges are on the side walls of the groove, so that the coupling electric field between the side wall of the groove of a first word line structure part 200A and the second word line structure part 200B of adjacent word line structure is reduced, the interference between the word line structures is reduced, and the performance and the reliability of a semiconductor device are improved.