Heteroanionic doping of metal oxide semiconductors enables unique optoelectronic properties as a result of the tunable bonding and variable charge transport properties imparted by diverse anion chemistry. Here the effects of fluoride (Fˉ) doping in an archetypical metal oxide semiconductor, indium oxide (In-O), is studied. Optimized Fˉ-doped In-O (F:In-O) thin films are characterized by a diverse suite of structural and spectroscopic methods, thus revealing the unique bonding character of fluorine in indium oxide. These experimental results are explained by differences in coordination number as confirmed by atomic-level theoretical calculations. This tailored bonding enhances the electronic properties of F:In-O films as manifested in enhanced switching ratios in thin-film transistors compared to undoped In-O films. These results establish heteroanionic doping as a novel pathway to enhancing the optoelectronic properties of metal oxide semiconductors.