The photoelectrochemical behaviour of p-Si(100) single crystal electrodes in aqueous solution, covered with a very thin nitride film, was studied. The silicon surface nitridation was achieved in a N-2-H-2 plasma at floating potential. The as-grown insulating Si3N4 layers, with thickness inferior to 3.1 nm, allow the electrons to tunnel in the presence of an electric field by the Fowler-Nordheim tunnelling mechanism. However, the p-Si(100)/Si3N4-electrolyte interface generated lower photocurrent densities than those generated by naked p-Si(100) electrodes. In contrast, the nitridated silicon surface displayed a significant stability improvement in aqueous electrolyte (neutral pH). An overvoltage higher than 0.6 V for water oxidation on a p-Si(100) covered with a 2.4 nm Si3N4 layer was measured. The results show that silicon covered with a nitridated thin film may be useful to stabilize electrodes in photoelectrochemical applications. 0 2007 Elsevier B.V. All rights reserved.