A method for manufacturing a semiconductor device is provided. The method includes operations below. First, an epitaxial layer is formed on a substrate. Then, a trench is formed in the epitaxial layer. Then, a first dielectric layer and a shield layer are formed in the trench, in which the shield layer is embedded within the first dielectric layer. Then, a spacer layer is formed in the trench and on the first dielectric layer. Finally, a second dielectric layer and a gate are formed in the trench and on the spacer layer, and a source is formed in the epitaxial layer surrounding the trench, in which the gate is embedded within the second dielectric layer, and the source surrounds the gate.