Various platinum (Pt) colloid solutions were prepared and used for the modification of n-type silicon (n-Si) electrodes. All the photoelectrochemical (PEC) solar cells, equipped with the Pt-colloid modified n-Si electrodes thus prepared, gave the open-circuit photovoltages (V(oc)) of 0.550 to 0.630 V, much higher than those (0.25 approximately 0.30 V) for n-Si electrodes coated with continuous thin Pt layers, clearly showing the beneficial effect of the discontinuous metal coating. The PEC cells, equipped with the textured-surface n-Si electrodes modified with the Pt colloid particles prepared by Bredig’s method, yielded an energy conversion efficiency of 14.9% in a three-electrode configuration. The relation between the V(oc) and the size and distribution of the Pt particles is discussed.