Surface plasmon resonance from noble metal nanoparticles is a promising way to improve the efficiencies of silicon based photodiodes and solar cells. Electroless plating is an extremely simple technique for producing such metallic nanoparticles. It is found that the deposition of gold on Si photodiodes occurs as chains that drastically reduce the photodiodes conversion efficiency. However, silver deposits as nano-islands that are efficient SPR centers, which improve the performance of Si photodiodes in the visible region: as measured by both IPCE and I-V curves. The greatest improvement observed was a 3.5% increase in J(sc) under solar irradiation. Although this improvement is lost upon annealing it can be regained by a further treatment in acidified HAuCl(4). Possible explanations for these latter two behaviors are proposed. (C) 2010 Elsevier B.V. All rights reserved.