In this study, ambipolar field-effect transistors (FETs) based on organic–inorganic bilayer structures were investigated. InO_x and pentacene were selected as n-type and p-type semiconductors, respectively. To improve the hole mobility, poly(perfluorobutenylvinylether) (Cytop) layer was introduced to modify the surface of InO_x. The ambipolar FETs showed hole and electron mobilities of 1.1 and 0.1 cm² V⁻¹ s⁻¹, respectively and excellent electrical stability under gate bias stress. Furthermore we found that ambipolar FETs could be integrated into functional complementary metal oxide semiconductor (CMOS)-like inverters and exhibited high peak gain (>50). This work provides a general method for realizing ambipolar FETs based on organic–inorganic hybrid structure.