A novel technique based in the combination of vapor silanization and chemical vapor deposition, hereafter referred to as activated vapor silanization (AVS), is shown to be an effective biofunctionalization technique. The AVS process results in thin organic films with a high surface amine concentration when deposited on substrates with different chemical characteristics, such as silicon, porous silicon, or gold. Chemical characterization shows that the films are composed of carbon (hydrocarbon, C–Si, C–C), silicon (different oxidation states), nitrogen (primary and secondary amines), oxygen, and hydrogen. Relevantly, the amines are also distributed along the film thickness, ensuring functionality even after some degradation of the films. AVS films behave practically as monocrystalline silicon substrates under loading–unloading tests. In addition, the AVS films behave as permeable membranes for molecules smaller than 5 Å, and the amine surface concentration is estimated to be 8 NH2/nm2 for molecules of about 12 Å, which is three times higher than that obtained with standard silanization procedures.