A semiconductor device includes a nonvolatile memory cell and a current detecting type sense amplifier for detecting a current flowing through a data line into the memory cell. The semiconductor device is further provided with an element for outputting a first voltage detecting signal when a detected supply voltage exceeds a set value and outputting a second voltage detecting signal when the detected supply voltage does not exceed the set value. The sense amplifier includes an element for switching a dependent characteristic of a level sensing current upon the supply voltage to be a higher response to the first voltage detecting signal. Thus, error reading of a data from the memory cell, which can be otherwise caused under application of a low supply voltage, can be avoided.