A memory device includes an access device including a first doped semiconductor region having a first conductivity type, and a second doped semiconductor region having a second conductivity type opposite the first conductivity type. Both the first and the second doped semiconductor regions are formed in a single-crystalline semiconductor body, and define a p-n junction between them. The first and second doped semiconductor regions are implemented in isolated parallel ridges formed in the single-crystal semiconductor body. Each ridge is crenellated, and the crenellations define semiconductor islands; the first doped semiconductor region occupies a lower portion of the islands and an upper part of the ridge, and the second doped semiconductor region occupies an upper portion of the islands, so that the p-n junctions are defined within the islands.