As the thickness of gate quality SiO2 is reduced, minor structural interface imperfections begin to play an important role in device performance and yield. To isolate the effects of a variety of such interface imperfections on electric field distribution within the SiO2 layer of biased metal oxide semiconductor capacitors, numerical calculations were carried out. The results indicate that strong electric field distortions may be expected for almost any interfacial defect configuration, being highest for metal precipitates. Technological consequences of the findings are also discussed.