Two soluble phthalocyanine derivatives, 2,9,16-tri(tert-butyl)-23-(10-hydroxydecyloxy) phthalocyanine (1) and 2,9,16-tri(tert-butyl)-23-(10-hydroxydecyloxy) copper phthalocyanine (2) were used as semiconductor layers in organic thin-film transistors (OTFTs) based on their Langmuir-Blodgett (LB) films. From the pi-A curves, we can conclude that the phthalocyanine 1 and 2 molecules are in a titled arrangement at the airwater interface. The molecular ordering in the LB multilayer films on the SiO2 substrate was examined by using UV-Vis absorption spectra and atomic force microscopy (AFM). The highest occupied molecular orbital and the lowest unoccupied molecular orbital were determined, and the energy band diagram of their OTFTs can be deduced by the cyclic voltammetric measurements. The LB films of phthalocyanine 1 and 2 were subsequently made into p-channel field-effect transistors, which were generally operated in the enhanced mode. The channel mobilities of phthalocyanine 1 and 2 were calculated to be about 4.8 x 10(-5) cm(2) V-1 s(-1) and 4.0 x 10(-4) cm(2) V-1 s(-1), respectively.