The thermal reaction of undecylenic acid with a hydrogen-terminated porous silicon surface takes place at 95degreesC to yield an organic monolayer covalently attached to the surface through Si-C bonds. The acid terminal group remains intact and is not affected by the chemical process. Under the same conditions, alcohols break the Si-Si back bonds of the PSi matrix. In contrast, the acid function does not react with either the Si-H or the Si-Si bonds of the PSi surface and the reaction takes place at the terminal C v C double bond of the molecule. When the reaction was carried out with decanoic acid, under the same conditions, the reaction was not complete. The functionalized surfaces were characterized using transmission infrared and X-ray photoelectron spectroscopies. The effect of the chemical process on the photoluminescence has been studied, and the stability against corrosion in 100% humidity was verified using chemography. We have demonstrated that the derivatized surface with undecylenic acid can be activated by a simple chemical route using N-hydroxysuccimide in the presence of N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide hydrochloride.