Semiconductor device and operating method thereof

A semiconductor device comprising:

• a memory string coupled between a source line and a bit line, the memory string including at least one first select transistor, a plurality of memory cells, and at least one second select transistor, wherein a channel region of the memory string includes a first channel region at one side of a selected memory cell among the plurality of memory cells and a second channel region at the other side of the selected memory cell;
• and
• a control logic configured to couple the memory string to the source line or the bit line, turn off a selected memory cell, increase a level of word lines coupled to unselected memory cells among the plurality of memory cells to a pass bias such that the first channel region and the second channel region have different potential levels, increase a level of a word line coupled to the selected memory cell to a pre-program bias greater than the pass bias, and apply a program bias to the word line coupled to the selected memory cell.