We present experimental tunneling current‐voltage characteristics for a wide (1040‐A˚‐wide well) double‐barrier structure; concomitant differential conductance data show a series of oscillations in the differential conductance‐voltage characteristics. By using a self‐consistent analysis, we show that the observed conductance oscillations arise predominantly from the structure of the local density of states of the confining well rather than the density of states of the global structure; this result shows that there is a lack of long‐range phase coherence for the tunneling electrons in this structure. Also, in this analysis we determine the importance of the band nonparabolicity.