A method of programming a nonvolatile semiconductor memory device using a negative bias voltage. The method includes turning ON the string selection transistors connected to selected bit lines and turning OFF the string selection transistors connected to unselected bit lines in the same memory block, in a program mode. This can be achieved by applying a negative bias voltage to a bulk substrate and applying a voltage having a voltage level higher than the threshold voltage of string selection transistors connected to selected bit lines and lower than the threshold voltage of string selection transistors connected to unselected bit lines. The method may reduce programming disturbance between a selected cell string and an unselected cell string.