An experimental technique for probing the minority-carrier quasi-Fermi level in epitaxial Schottky-barrier diodes has been developed and verified for the first time. The technique uses a novel self-aligned floating guard ring as a probe for the hole quasi-Fermi level in the quasi-neutral epitaxial region of an epitaxial Schottky-barrier diode . The anode of the Schottky diode is separated from the guard ring by a thin sidewall oxide, thereby allowing the guard ring to be electrically isolated from the anode. It is shown through both simple physical arguments and two-dimensional numerical simulations that the potential on the floating guard ring assumes the value of the plateau of constant-hole quasi-Fermi level in the quasi-neutral epitaxial region under the anode when bias is applied to the anode. Experimental measurements on both low- and high-barrier Schottky diodes agree very well with two-dimensional numerical simulations as well as computer simulations of a detailed equivalent-circuit model. The result provides direct evidence of the fact that the hold quasi-Fermi level in the silicon does not line up with the metal level at large forward bias and indicates that Schottky-barrier diodes can be scaled further than previously predicted. © 1985 IEEE.