The influence of electron energy width in the hot electron double-slit experiment is investigated quantitatively. The required condition on the Fermi level in the emitter and the slit-spacing is derived for the experiment. In order to achieve a coherent electron source, a single-barrier graded emitter structure is discussed and its characteristics are considered. For application to the hot electron double-slit experiment, the graded emitter diode is fabricated and the current–voltage relation is measured in a supplementary experiment. ©1997 American Institute of Physics.