AbstractPlatinum (Pt) nanocatalysts were deposited on/inside of nanostructured silicon (nanoSi) matrix using physico‐chemical methods, i.e. E‐beam high vacuum Pt thin film and, respectively, chemically loaded Pt nanoparticles from hexachloroplatinic acid aqueous or alcoholic precursor solutions. High resolution morphological characterisations, completed by microstructural and compositional analyses have been performed to characterise the nanoSi catalyst support and to investigate the Pt thin film nanostructuration as well as the nanoparticle attachment and clustering processes, evidencing the controlling factors and conditions of the size, morphology and distribution. Furthermore, the experimental structures have been subjected to different electrochemical tests and it was revealed that significant improvement of the long term catalyst stability was achieved when the metal‐porous Si nanoassemblies is formed, which represents a step closer to the realisation of the monolithic integrated Si‐based microfabricated fuel cell.