A new negative‐resistance device, the semiconductor—insulator—semiconductor or SIS structure, is analyzed. The effect is due to quantum‐mechanical current transmission through a thin insulator barrier and leads to an N‐shaped current—voltage characteristic similar to that of the tunnel or Esaki diode. A highly qualitative analysis using general current equations is used to predict the major characteristics. Among these is the fact that the height and shape of the potential barrier, as created by the insulator, influence the current—voltage characteristics significantly—the former controls the amount of diffusion current and the latter the shape of the tunnel‐current characteristic. Diffusion currents should be negligibly small as compared to those in the conventional tunnel diode because the barrier height is very high (∼5 eV) for most typical insulators. These and other features, such as wider adjustment of the negative‐resistance cutoff voltage through variation in impurity concentration, give the SIS structure enormous versatility in terms of current—voltage shape adjustment through material control. A crude calculation, using the Wannier formalism, is used to derive an expression for the current in a simple, closed analytic form. This analysis shows that, at low temperatures, the slope of current characteristic (dJ∕dVA) is a function of the insulator energy gap, ΔI, and will usually be less than that for the equivalent tunnel diode. The general conclusion reached is that realization of the SIS diode is perhaps just beyond the scope of current semiconductor technology. Nevertheless, if developed properly, this structure could conceivably find wide application in current MOS integrated circuits.