The electroless deposition of Pt nanoparticles (NPs) on hydrogen-terminated silicon (H-Si) surfaces is studied as a function of the temperature and the immersion time. It is demonstrated that isolated Pt structures can be produced at all investigated temperatures (between 22 and 75 degrees C) for short deposition times, typically within 1-10 min if the temperature is 45 degrees C or less than 5 min at 75 degrees C. For longer times, dendritic metal structures start to grow, ultimately leading to highly rough interconnected Pt networks. Upon increasing the temperature from 22 to 75 degrees C and for an immersion time of 5 min, the average size of the observed Pt NPs monotonously increases from 120 to 250 nm, and their number density calculated using scanning electron microscopy decreases from (4.5 +/- 1.0) X 10(8) to (2.0 +/- 0.5) x 10(8) Pt NPs cm(-2). The impact of both the morphology and the distribution of the Pt NPs on the photoelectrocatalytic activity of the resulting metallized photocathodes is then analyzed. Pt deposited at 45 degrees C for 5 min yields photocathodes with the best electrocatalytic activity for the hydrogen evolution reaction. Under illumination at 33 mW cm(-2), this optimized photoelectrode shows a fill factor of 45%, an efficiency (eta) of 9.7%, and a short-circuit current density (\J(sc)\) at 0 V versus a reversible hydrogen electrode of 15.5 mA cm(-2).