Provided is a semiconductor device including a substrate and a stack layer. The substrate includes a first region, a second region, and a third region. The third region is disposed between the first region and the second region. Since a top surface of the substrate in the first region is lower than the top surface of the substrate in the second region, the substrate in the third region has a first step height. The stack layer is disposed on the substrate in the first and third regions. The top surface of the stack layer in the first region and the third region and the top surface of the substrate in the second region are substantially coplanar.