Aging effects in In 2O 3/SiO 2/Si semiconductor/insulator/semiconductor (SIS) solar cells were investigated using scanning Auger microscopy (SAM) and depth profiling. Single-crystal, 〈111〉 oriented, p-type substrates of silicon were used in this study. The i layer (SiO 2) was thermally grown at 1000 °C in an oxygen atmosphere, to a thickness of approximately 800 Å. Thin films of In 2O 3 were deposited by the evaporation of indium in an oxygen atmosphere. Auger depth profiling revealed that the initial thickness of the SiO 2-Si interface was about 34 Å which increased to approximately 80 Å over a period of six to eight weeks. A trace of unoxidized silicon was also observed throughout the SiO 2 layer in the freshly prepared sample. This silicon was almost completely oxidized after aging and a noticeable increase in the thickness of the SiO 2 layer was observed.