A semiconductor device includes an inter-metal dielectric layer, a memory cell, a transistor and a dielectric layer. The memory cell includes a metal-insulator-metal (MIM) structure over a top surface of the inter-metal dielectric layer. The transistor underlies the inter-metal dielectric layer. The dielectric layer extends over the transistor and along the top surface of the inter-metal dielectric layer. The dielectric layer is separated from the MIM structure.