STM images of DNA molecules on gold substrate display contrast inversions both while adjusting current-setting and spontaneously. Such a feature turns out to be associated with long-range characteristics in the tunneling-distance spectroscopy that is not explainable within the WKB formulation, the widely used semiclassical theory for fitting STM images. Here we render a picture, compatible with the experimental observations, by suggesting a model for resonant tunneling through structured vacuum levels formed by the DNA as a macro-charged-polyelectrolyte.