We present results of the excimer laser wet oxidisation of submicron thick hydrogenated amorphous silicon films (a‐Si:H) deposited on silicon wafer. The a‐Si:H film irradiation was carried out by multiple‐pulses, large‐spot, 20 ns KrF (248 nm) excimer laser and fluences of 140‐300 mJ/cm2, near to the silicon ablation threshold in an air atmosphere. The oxygen and hydrogen content and bonding in the thin films were analysed by Fourier Transform Infrared Spectroscopy (FTIR) techniques in the range 400‐4000 cm–1. We demonstrate that the presence of water molecules on the silicon surface will increase oxidation by 30‐40%. The bonded hydrogen content in the films after oxidation annealing is decreased from 12 down to around 1 atomic percent. Wet oxidised surfaces present highly hydrophobic properties which appears to be determined by the amorphous silicon structure transformation and silicon surface energy modification forming a silicon/oxide (nitride) interface. (© WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)