The chemical composition and interface structure of silicon on insulator (SOI) formed by O+ (200 keV, 1.8×l018/cm-2) or N+ (190 keV, 1.8×1018/cm-2) implanted into silicon have been investigated by using Auger electron spectroscopy (AES) with in situ sputtering. For SOI structure produced by O+ implantation and annealing at 1300℃ for 5 hours, the characteristic Auger spectrum for the interface between the top silicon layer and the buried oxide layer was measured and a chemical state of silicon was identified, whose major transition was at 85 eV, different from that of the bulk silicon or silicon in SiO2. This chemical state was also discovered in the buried oxide layer. For SOI structure produced by N+ implantation and annealing at 1200℃ for 2 hours, a nitrogenrich porous layer was observed in the buried nitride layer. For both SOI structures, the strong asymmetry of the two main interfaces was observed. These results are in agreement with the results of infrared absorption (IR) analysis and transimission electron microscopy (TEM) analysis. The detailed explanation of these results is also presented in this paper.