Here we review various modifications of silicon dioxide as a gate dielectric layer – bare surface as well as modification by the self-assembled monolayer of hexamethyldisilazane, poly(methyl methacrylate), or a blend of poly(methyl methacrylate) with poly(4-vinyl phenol) and cross-linked poly(4-vinyl phenol). The impact on electric properties is investigated for organic complementary inverters with pentacene and fullerene C60 as semiconductive materials. Here we discuss basic principles presented in gate dielectric layers as geometry, free surface energy, leakage current and electron traps.