In this study the electrical stability of solution processed metal-oxide thin-film transistors (MOTFTs) is improved by an yttrium oxide (Y2O3) passivation layer. Therefore, we tailored a simple Y2O3 sol-gel process towards a thin, smooth and continuous film. For a 0.1 M Yttrium(III) nitrate hexahydrate solution gelatinized for 5 h, pre-converted in an UV/O3 cleaner (t = 40 min) and thermally converted at T = 350 °C a root-mean-square (RMS) roughness of 0.1 nm is determined. The refractive index is 1.9 and corresponds to the reported value in literature (n = 1.9 [1]). Finally, we compare MOTFTs passivated by a) octadecylphosphonic acid (ODPA), b) the sol-gel derived Y2O3 and c) an Y2O3 layer from atomic layer deposition (ALD). The field-effect mobility is not significantly affected by the passivation layer and the onset voltage of MOTFTs passivated with a sol-gel derived Y2O3 layer amounts desirable 0 V. The onset voltage shift during negative-bias-stress (NBS) amounts to ?Von,Y2O3 = -2 V for MOTFTs with a sol-gel Y2O3 passivation layer and is five times smaller compared to MOTFTs with a solution-processed ODPA passivation layer (?Von,ODPA = -10 V). The quality is comparable to MOTFTs passivated by Y2O3 with a cost-intensive ALD process (?Von,ALD = -2 V).