Information about the local environment of dopants in semiconductor materials is required to understand and help optimize the electrical activity in highly doped samples. The near-edge (XANES) and extended x-ray absorption fine structure (EXAFS) components of x-ray absorption spectra provide detailed information on local geometric and electronic structure about selected atoms. Electron yield and fluorescence detection of As K EXAFS and XANES, with sample rotation to eliminate substrate diffraction, have been used to study the As sites in Si(As) epilayers grown by molecular-beam epitaxy (MBE) and doped in situ by low-energy As implantation. Marked differences are found in both the near edge and EXAFS signals between samples prepared under low temperature (460 °C) growth/implantation conditions and those prepared under the preferred, higher temperature (700 °C) growth conditions. The EXAFS analysis indicates that As is located primarily in the substitutional site in the optimal (700 °C) sample but that a large fraction of the As is in a defect site, with possibly some incorporated as some type of As–As clusters in the samples grown at 460 °C.