A memory device includes a lower conductive line, a first memory unit, a second memory unit, and a shared lower electrode including first and second portions electrically connecting respective ones of the first memory unit and the second memory unit to the lower conductive line. A first insulating region is disposed between the first and second memory units. A second insulating region is disposed on the first insulating region. The device further includes a first switch unit on the first memory unit and including an upper electrode with a portion protruding from the second insulating region and a second switch unit on the second memory unit and including an upper electrode with a portion protruding from the second insulating region. First and second upper conductive lines contact the protruding portions of the respective upper electrodes.