We report a vapor-phase molecular layer deposition (MLD) of self-assembled multilayer thin films for organic thin-film transistor. In the present MLD process, alkylsiloxane self-assembled multilayers (SAMs) were grown under vacuum by repeated sequential adsorptions of C=C-terminated alkylsilane and aluminum hydroxide with ozone activation. The MLD method is a self-controlled layer-by-layer growth process, and is perfectly compatible with the atomic layer deposition (ALD) method. The SAMs films prepared exhibited good mechanical flexibility and stability, excellent insulating properties, and relatively high dielectric capacitances of 374 nF/cm2 with a high dielectric strength of 4 MV/cm. They were then used as a 12 nm-thick dielectric for pentacene-based thin-film transistors (TFTs), which showed a maximum field effect mobility of 0.57 cm2/V s, operating at -4 V with an on/off current ratio of approximately 10(3).