We analyze the current density‐voltage characteristics of double‐barrier tunneling diodes, with different spacer layers, within the framework of a Poisson solver together with a coherent tunneling approximation for transmission probabilities. We show that varying the spacer layer thickness, together with barrier heights, changes dramatically the current density‐voltage characteristics line shape, which is revealed to be an important qualitative signature of the tunneling paths involved in the double‐barrier diodes under operation. ©1995 American Institute of Physics.