This work presents additional arguments about the enhancement of optical and electrical properties of SiNWs obtained by chemical etching and the beneficial effect of the formation of ultrathin film of SiO2 by a heat treatment at 900 and 1000 °C reported recently by Karyaoui et al. in [Eur. Phys. J. Appl. Phys. 58, 20103 (2012)]. In the actual study, we report the effect of this thermal oxidation treatment on the morphological and optoelectronic properties of silicon nanowires (SiNWs). The SEM and AFM observations exhibit indeed a remarkable change of the surface shape after this oxidation. On the other hand, the LBIC measurements of the SiNWs reveal that the thermal treatment improves the optoelectronic response at 900 °C and the effective diffusion length increases from 150 μm for untreated SiNWS to 235 μm after thermal treatment.