Abstract: The present application discloses a semiconductor device and a method for making the same. The semiconductor device includes a substrate, a word line, a word line dielectric layer, and first and second source/drain regions. The word line is buried in the substrate. The word line dielectric layer is disposed between the substrate and the word line, and the word line dielectric layer includes: a first oxide layer and a second oxide layer. The first oxide layer is in contact with the word line and is formed by an atomic layer deposition (ALD) process. The second oxide layer is in contact with the substrate and is formed by a thermal oxidation process. The first and the second source/drain regions are disposed in the substrate and above the word line, wherein the word line is disposed laterally between the first and the second source/drain regions.