Transistor, memory cell array and method for forming and operating a memory device

A substrate forming an array of vertical transistor cells for selecting one of a plurality of memory cells and wherein each memory cell couples a transistor to a bit line via a memory element and is addressable by selecting two word lines and a bit line is disclosed. For minimizing the area of a cell and reducing complexity in production, one word line trench takes one word line, wherein in a first embodiment a first word line in a first word line trench forms a plurality of gate electrodes on one sidewall of active areas of a first and a second, adjacent row of transistor cells in word line direction, and wherein a second word line in an adjacent word line trench forms a plurality of gate electrodes on the opposite sidewall of active areas of the second and of a third row of transistor cells in wordline direction.