A memory device includes a first bottom electrode, a first memory stack, and a second memory stack. The first bottom electrode has a first portion and a second portion connected to the first portion. The first memory stack is over the first portion of the first bottom electrode. The first memory stack includes a first resistive switching element and a first top electrode over the first resistive switching element. The second memory stack is over the second portion of the first bottom electrode. The second memory stack comprises a second resistive switching element and a second top electrode over the second resistive switching element.