Semiconductor memory devices having selection transistors with nonuniform threshold voltage characteristics

A semiconductor memory device, comprising:

• an active pattern disposed on a semiconductor substrate, and extended toward a direction far away from the semiconductor substrate;
• and
• a lower selection gate controlling a first channel region that is defined at the semiconductor substrate and a second channel region that is defined at a lower portion of the active pattern,
• wherein a first threshold voltage of the first channel region is different from a second threshold voltage of the second channel region.