Por-Si surface studies were carried out by Auger electron spectroscopy (AES), thermostimulated exoelectron emission (TSEE), photoluminescence (PL) in visible region and ellipsometry. The spectra of visible luminescence, dependences of refractive index of surface layers on porosity were investigated. The AES and TSEE have been applied for studies of per-Si surface. The elemental composition and thickness of thin films of natural oxide and created in the result of electrochemical etching and further contact with gaseous phase per-Si were analyzed by quantitative AES. Effective thickness of SiyOxC1-x-y thin film coatings and their composition after different electrochemical etching regimes and, consequently, per-Si porosity have been evaluated. The SiyOxC1-x-y, coatings thickness raise with increasing of per-Si porosity. The dielectric amorphous thin films oxygen-carbon coatings might play a significant role in PL of per-Si.