Nonvolatile memory devices, read methods thereof and memory systems including the nonvolatile memory devices

A reading method of a nonvolatile memory device including a plurality of strings on a substrate, each one of the plurality of strings being perpendicular to the substrate and including a plurality of memory cells stacked in a direction perpendicular to the substrate, the reading method comprising:

• applying a bit line voltage to a selected bit line among a plurality of bit lines, the selected bit line connected to a selected string among the plurality of strings;
• applying a first string selection line voltage to at least one selected string selection line connected to the selected string;
• applying a second string selection line voltage to at least one unselected string selection line connected to unselected strings among the plurality of strings;
• applying at least one read voltage to a plurality of word lines connected to the plurality of strings;
• applying a first ground selection line voltage to at least one selected ground selection line connected to the selected string;
• and
• applying a second ground selection line voltage to at least one unselected ground selection line connected to unselected strings among the plurality of strings,
• wherein each one of the plurality of strings includes the plurality of memory cells on a ground selection transistor, and a string selection transistor on the plurality of the memory cells.