A semiconductor structure and a method for forming the same are provided. The semiconductor structure comprises a substrate, a first source/drain region, a second source/drain region, a first stack structure and a second stack structure. The first source/drain region is formed in the substrate. The second source/drain region is formed in the substrate. The first stack structure is on the substrate between the first source/drain region and the second source/drain region. The first stack structure comprises a first dielectric layer and a first conductive layer on the first dielectric layer. The second stack structure is on the first stack structure. The second stack structure comprises a second dielectric layer and a second conductive layer on the second dielectric layer.