Fluorographene (FG) ultrathin films are directly grown on flexible and nonflexible insulating silicate substrates and characterized in terms of their structural and electronic properties. FG is identified as an in-plane heterostructure consisting of sp² and sp³ carbon domains. Solid-state ¹⁹F NMR shows that fluorine is mainly localized in spaces adjacent to sp² carbon domains, which can be explained by a more uniform fluorine distribution in the boundaries between small sp² and sp³ domains, rather than by an accumulation of fluorine in large sp³ patches, and which is supported by Raman spectroscopy. The fluorine doping is further confirmed by spectroscopic ellipsometry studies, where it showed a band gap of 1.2 eV for thin-film FG, which is found to be consistent with density-functional-theory-based calculations for graphene layers doped with similar amounts of fluorine. Furthermore, this semiconducting FG layer grown with a large surface area has been identified as an ambipolar material from gate-controlled transport measurements, with holes being the majority of charge carriers. The transport properties of thin-film FG resemble those of reduced graphene oxide, another functionalized graphene derivative, with an Arrhenius-type temperature dependence of the resistance at high temperatures. This study opens up the possibilities of atomic-layer-based electronic circuitries and biosensors, where FG can be used as an active layer or dielectric support by tuning its fluorine content to the requisite level.