Fourier transform infrared spectroscopy (FTIR) was used to investigate the reaction of methanol with porous silicon and hydrogen passivated porous silicon. At 300 K methanol adsorbs onto hydrogen free porous silicon by cleavage of the O-H bond. Both of the resulting surface species, Si-H and Si-OCH3, were determined to be stable up to ∼500 K. Above 500 K the Si-OCH3 moiety decomposes by breakage of the C-O and C-H bonds. The resulting carbon and oxygen were incorporated into the porous layer and additional Si-H surface species were detected. Further heating to 900 K removed the Si-H surface species. Adsorption of methanol onto hydrogen-passivated porous silicon did not occur until 600 K. At temperatures beyond 600 K, oxygen and carbon incorporation into the porous layer and Si-OCH3, Si-CH3, and Si-H surface species were seen. The previously unseen Si-CH3 surface species is believed to be stabilized by oxygen incorporation.