In a nonvolatile semiconductor memory according to the invention, a power source voltage of 5 V used in an ordinary read mode is applied to a read line in the data read mode without changing its value. If a write line, a selection gate line, a control gate line, and a read line are respectively set at 0 V, 5 V, 0 V, and 5 V in the data read mode, the potential at an n-type diffusion layer becomes 0 V. In this case, the potential at the control gate line is 0 V, and the potential at a floating gate electrode becomes substantially 0 V. That is, an electric field is not applied to a thin insulating film located between the floating gate electrode and the n-type diffusion layer. As a result, electron injection and discharge due to the tunnel effect do not occur.