Provided is a semiconductor device. Two stack layers are disposed on a substrate of a first conductivity type. Each of stack layers includes a dielectric layer and a conductive layer. The dielectric layer is disposed on the substrate. The conductive layer is disposed on the dielectric layer. First doped region of a second conductivity type has a first dopant and is disposed in the substrate between the stack layers. A pre-amorphization implantation (PAI) region is disposed in the first doped region. A second doped region of the second conductivity type has a second dopant and is disposed in the PAI region. The first conductivity type is different from the second conductivity type. A diffusion rate of the second dopant is faster than a diffusion rate of the first dopant, and a thermal activation of the second dopant is higher than that of the first dopant.