The first stages of platinum electroless deposition on (100) Si from hydrogen fluoride solutions are studied by tapping mode atomic force microscopy (AFM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS). Tapping mode AFM and TEM provide a morphological characterization of the samples, while XPS accounts for the compounds present on the surface. During immersion in an aqueous HF solution containing a platinum salt, platinum nucleates on the silicon substrate while the surface is etched. The deposited nuclei are polycrystalline, highly pure, and strongly silicidated at room temperature. Metal deposition takes place by means of a redox reaction in which silicon atoms oxidize, supplying the electrons for the metal to reduce. For all substrates, platinum silicide is formed during deposition at room temperature, suggesting a competition between the deposition of pure metal by an electrochemical mechanism and the formation of the silicide by direct reaction. For equal deposition times, more platinum deposits on p-type substrates than in n(+). p-Type substrates, moreover, undergo a general increase in roughness in the bare silicon areas, while n-type substrates present a lower and more local etching. This seems to indicate that electroless platinum deposition is somehow hindered on nt substrates.