A read operation on selected memory cells may be performed by a method of operating a semiconductor memory device. The method may include determining a read voltage to be used in the read operation among first to 2N−1-th read voltages, applying the determined read voltage to a selected word line connected to the selected memory cells, and applying a read pass voltage to unselected word lines based on whether the determined read voltage is a first read voltage. Here, N may be a natural number of 2 or more.