Positively and negatively charged defects and dopant atoms in n-doped GaAs(110) surfaces give rise, at room temperature, in occupied-state scanning tunneling microscope images to a bright elevation, which is surrounded by a dark depression ring. This oscillating contrast is not observed in empty-state images. A similar effect is found on n-doped GaP(110) surfaces. A simulation of the contrast induced by localized charges on (110) surfaces of III-V semiconductors suggests that the oscillation in room-temperature scanning tunneling microscope images can be explained as the image of the local potential change (screened Coulomb potential) induced by the presence of the charge.