Many experimental and some theoretical studies on two terminal devices in the form metal(1)vertical bar semiconductor vertical bar metal(2) report on unusual I-V relations which exhibit hysteresis and crossing of the I-V curve under periodic applied voltage. It is believed that the semiconductors allow also for motion of ionic defects and they are thus, mixed-ionic-electronic-conductors (MIECs). The device simulated here is of the form metal(1)vertical bar MIEC vertical bar metal(2) where the thin semiconductor layer is n-type and the donors are mobile. The applied voltage is periodic. It is limited so that the temperature is constant. The conduction electrons are coupled to the mobile donors via the Poisson equation thus the redistribution of donors under an applied voltage leads to dramatic changes in the device's resistance. The donors considered are native ones and the electrodes allow exchange of matter with the surroundings which affects the I-V relations. The results suggest that a necessary condition for I-V curve crossing is an asymmetry in the device or in the applied voltage. (C) 2013 Elsevier B.V. All rights reserved.