We present extended x-ray absorption fine structure (EXAFS) analyses of the Er LIII edge in Er-doped (100) Si samples. The samples were prepared by multiple implants of Er and O resulting in the incorporation of 1×1019 Er/cm3 and 1×1020 O/cm3 in a 2.3-μm-thick amorphous layer. It has been found that the local environment around the Er sites, which consists of six Si first neighbors in the amorphous layer, evolves towards a mixed coordination with O and Si atoms after epitaxial regrowth of the layer at 620 °C for 3 h. A further thermal treatment at 900 °C removes the residual Er–Si coordination and produces a full oxygen coordinated first shell with an average of 5 O neighbors. The effects of the different thermal processes on the high resolution spectra of the 1.54 μm Er photoluminescence were also measured and related to the EXAFS results. © 1997 American Institute of Physics.