Electroformed metal-insulator-metal structures showing negative differential resistance, electron emission and electroluminescence can be created by applying a high voltage to an ultra-thin conducting film. The physical processes causing these phenomena are not fully understood although the significance of such factors as the composition of the residual vacuum under which measurements arc made has been recognized. The interpretation of the effects is difficult due to the nonlinearity of the electrical characteristics and the unavoidably large intrinsic film resistance. The influence of the nonlinear characteristics on the interpretation of previously reported data from experiments on noise, transient currents, electron emission and peak currents is discussed. The position of the current peak and the form of the low voltage current-voltage characteristic are also illustrated experimentally. It is suggested that the initial film resistance can be used to obtain estimates of the form of the curve and the position of the intrinsic current peak. Furthermore, it is proposed that the deliberate introduction of external series resistance can be used to separate the low-field electron emission from the electroluminescence more clearly.