Polymer doping of solution-processed In2O3 with small amounts of the electron-rich polymer, polyethylenimine (PEI), affords superior transistor performance, including higher electron mobility than that of the pristine In2O3 matrix. PEI doping of In2O3 films not only frustrates crystallization and controls the carrier concentration but, more importantly, acts as electron dopant and/or scattering center depending on the polymer doping concentration. The electron donating capacity of PEI combined with charge trapping and variation in the matrix film microstructure yields, for optimum PEI doping concentrations of 1.0%-1.5%, electron mobilities as high as approximate to 9 cm(2) V-1 s(-1) on a 300 nm SiO2 gate dielectric, an excellent on/off ratio of approximate to 10(7), and an application optimal V-T. Importantly, these metrics exceed those of the pure In2O3 matrix with a maximum mobility approximate to 4 cm(2) V-1 s(-1). Furthermore, we show that this approach is extendible to other oxide compositions such as IZO and the technologically relevant IGZO. This work opens a new means to fabricate amorphous semiconductors via solution processing at low temperatures, while preserving or enhancing the mobility of the pristine polycrystalline semiconductor.