Grazing incidence small angle X-ray scattering was used with synchrotron beam to determine lateral pore sizes and distances between pores formed by anodizing thin (similar to300 nm) surface layers of p-type silicon substrates with different current densities, electrolyte compositions, and temperatures. The diffuse scattering was recorded by a two-dimensional gas-filled detector and showed an intensity distribution compatible with a pore correlation parallel to the porous silicon layer. This was observed for all the samples irrespective of their anodization conditions. The experimental intensity data were reproduced by assuming a model of spherical pores. The depth profiles of the average pore diameters and interdistances parallel to the surface were obtained and compared with the mean layer porosities determined by previous specular X-ray reflectivity measurements made on the same samples. (C) 2003 The Electrochemical Society.