An anomalous field-oxide-growth phenomenon in a recessed local oxidation of silicon (LOGOS) structure with a nitride spacer (R-LOCOS), in which the field oxide growth at the center of the opening area is suppressed when isolation spacing is small, is reported. The field-oxide-ungrowth (FOU) phenomenon was found to have strong structural dependence, on the aspect ratio of the opening area, active pattern density, and silicon recess depth. By changing process conditions, such as dry etching and wet cleaning conditions, however, the FOU was not affected. Since the tendency of the FOU occurrence was coincident with that of the microloading effect in reactive ion etching, the FOU was believed to originate from a residue on the exposed silicon surface after the etching process. When silicon was not recessed, the FOU was not observed at any of the structural variations. From a two-dimensional simulation of field oxidation, it has been found that in a nonrecessed LOGOS structure, a residue on the silicon surface does not significantly affect field oxide growth, but in the recessed LOGOS structure, field oxide growth is very sensitive to the existence of a residue on the recessed surface. Thus, to successfully use the recessed LOGOS structure with a subquarter micron design rule avoiding the occurrence of the FOU, structural factors that include an active pattern layout should be carefully chosen.