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Formation of Si nanowire (SiNW) arrays using top-down methods based on metal-assisted chemical etching of Si is reported. Three different approaches were tested: i) a two-step process consisting in the electroless deposition of Ag nanoparticles followed by HF/H2O2 etching; ii) simultaneous electroless Ag deposition and etching in HF and highly concentrated AgNO3; iii) a multi-step process using an Au replica mask obtained by Au evaporation on Si samples covered with polystyrene spheres, followed by HF/H2O2 etching. The morphologies of the Si structures obtained in each case are discussed in terms of the influence of different parameters. The third approach led to well controlled etching. Depending on the polystyrene sphere size, Si pillars 1 µm or SiNWs 200 nm in diameter could be obtained.