A semiconductor device includes a random access memory (RAM) structure and a dielectric layer. The RAM structure is over a substrate and includes a bottom electrode layer, a ferroelectric layer over the bottom electrode layer, and a top electrode layer over the ferroelectric layer. The dielectric layer is over the substrate and laterally surrounds a lower portion of the RAM structure. From a cross-sectional view, the bottom electrode layer of the RAM structure has a lateral portion and a vertical portion, and the vertical portion upwardly extends from the lateral portion to a position higher than a top surface of the dielectric layer.