In this work we studied the self-assembled monolayer (SAM) formation of 3-mercaptopropyltrimethoxysilane HS(CH 2) 3Si(OCH 3) 3 (MPS) and 3-aminopropyltrimethoxysilane H 2N(CH 2) 3Si(OCH 3) 3 (APS) on platinum surfaces. We used X-ray photoelectron spectroscopy (XPS), specular reflectance FTIR, and electrochemistry to study the composition and structure of the self-assembly. XPS results of the Pt modified electrodes showed the presence of sulfur and nitrogen binding energy peaks indicating the presence of MPS and APS. The platinum substrates modified with MPS and APS showed IR absorption bands corresponding to the different stretches present in both compounds. Platinum disk electrodes, before and after being submerged in 1 mM solutions of MPS and APS for 24 h, were characterized voltammetrically by using 2.5 mM K 4Fe(CN) 6 in 0.1 M KCl, as the redox active couple. The MPS/Pt system is free of mass transfer effects, which are characteristic of pinhole defects in an MPS monolayer.