Si1−xMnx diluted magnetic semiconductor films were deposited on p-type Si(100) substrate by radio frequency magnetron sputtering method. Post thermal annealing was performed in an argon atmosphere at 1073K for 300s and at 1473K for 120s. The as-grown sample exhibits ferromagnetism at room temperature. Ferromagnetism is enhanced after annealing treatment. High resolution transmission electron microscopy shows that only Mn4Si7 compound formed in all samples. X-ray diffraction patterns and Fast Fourier Transform image indicate Mn atoms incorporated into Si lattice upon annealing. X-ray absorption fine structure suggests the formation of substitutional–tetrahedral interstitial Mn–Mn and tetrahedral interstitial–substitutional–tetrahedral interstitial Mn–Mn–Mn complexes in the 1473K annealed sample, which possesses the strongest ferromagnetism.