into a non oscillating state thus a logic memory element is obtained which can perform logic operations in dependence upon the signal applied to the control element the above described provision of metallic layer 5 can be carried out in any of various ways such as providing it only on one side or on both sides of a planar semiconductor element 1 or around the peripheral surface of a cylindrical semiconductor element 1a as shown in fig3 a or the layer 5 can be provided along substantially the whole longitudinal length or along one part of the longitudinal length otherwise the negative resistance diode is further provided with a pair of output terminals 7 and 8 as shown in fig3 c so that they are attached reactively at the portions near the electrodes 2 and 3 respectively whereby the output from the diode may be taken out of the terminals 7 and 8 for the purpose of enabling skilled persons in the art to understand and readily reduce this principle in practice the following actual example is shown a planar gaas semiconductor element was prepared from material of doping density n o 6 u00d7 10 13 cm 3 and mobility of 8 000 cm 2 vs in a dimension.