This paper investigates the effects of surface passivation in porous silicon (PS) as a hydrogen gas sensor. Two types of sample have been prepared, one with typical HF anodizing solution and the other with the presence of peroxide (H2O2) in the solution. The Fourier transform infrared (FT-IR) measurements on the PS layer on the Si substrate showed that the typical PS surface is characterized by chemical species like Si-H and Si-O. Samples anodized with peroxide based (H2O2) solution showed a PS structure with higher porosity (similar to 80%) and better surface passivation (higher concentration of Si-O and Si-H species) compared to those not treated with peroxide. Peroxide based PS sample fabricated as an H-2 gas sensor showed better electrical (I-V) sensitivity compared to those without peroxide, which has been associated with good surface passivation. Surface passivation in peroxide based PS is also maintained at higher temperatures (100 degrees C). (C) 2008 Elsevier Ltd. All rights reserved.