Using the recursive-Green-function (RGF) technique, we investigate the surf
ace states of an electrified binary semiconductor, modelled by a chain of a
lternating s and p orbitals. The RGF provides the surface density of states
(SDOS), which displays a quasi-Stark-ladder distribution of the energy lev
els in the two bands at the surface atom. The SDOS are discussed in terms o
f the applied-field and surface-perturbation parameters.