A very-low density (≪1010 cm-2) residual discrete energy-level interface trap at 228 meV from the Si midgap is detected on crystalline silicon covered by thermally grown oxide. Three signatures pointing to discreteness are delineated in the experimental data of the gate voltage modulation of the dc steady-state electron-hole recombination rate. Using the Shockley-Read–Hall recombination kinetics, the energy level is shown to have a linewidth less than 20 meV. From the present and previous data, the dopant impurity origin of this residual interface trap species is speculated rather than the amphoteric silicon dangling bonds. © 1999 American Institute of Physics.