The m.n.o.s. transistor has gained widespread acceptance as a nonvolatile memory element. In the present paper, we examine the switching properties of the m.n.o.s. transistor by comparing the experimentally determined oxide injection current to theoretically calculated oxide currents. On basis of this investigation, we present some calculated curves from which the switching properties can be predicted for the range of gate voltages normally used for writing. Furthermore, it is shown that the switching properties at low gate voltages depend entirely on the trap density and distribution in the nitride. Usually, it is desirable to minimise the swtiching for low gate voltages. A discussion of the requirements that this imposes on the trap distribution is presented