Flexible insulating materials that are both thermally and mechanically stable, highly transparent, and have low dielectric constants are highly desirable for electronic applications. With these technical needs, a highly disperse inorganic matrix is the most important factor in polyimide–inorganic composites. We report an optimised method for the preparation of a hyperbranched polyimide using HBPI_{BPADA-TAP(Si)}. This method involves modifying the polymer termini by coupling (3-isocyanatopropyl)triethoxysilane to HBPI_{BPADA-TAP(OH)} via the hydroxyl (–OH) groups at peripheral positions of the polymer chain. Then, based on the HBPI_{BPADA-TAP(Si)} with silane-modified termini, linear PI_6FDA-APB(Si) and tetraethoxysilane cross-linking agent were used to prepare ternary composites, PI_6FDA-APB(Si)_HBPI_{BPADA-TAP(Si)}_SiO₂, by sol–gel cross-linking reaction. The dielectric constant (D_k) of PI_6FDA-APB(Si)_HBPI_{BPADA-TAP(Si)}-30%_SiO₂-20% was very low, 2.04, and the optical transparencies of the ternary hybrid composite films also improved over those of similar composites due to the synergistic interactions between HBPI_{BPADA-TAP(Si)} and PI_6FDA-APB(Si) that improves phase dispersion. The highest transparency, 95% at 450 nm, was obtained for PI_6FDA-APB(Si)_HBPI_{BPADA-TAP(Si)}-30%_SiO₂-20%, a significant improvement from that (87%) of the binary composite of PI_6FDA-APB(Si)_SiO₂-20%. The glass transition temperature (T_g) of PI_6FDA-APB(Si)_HBPI_{BPADA-TAP(Si)}-30%_SiO₂-20% is 212.6 °C, which is the highest in the ternary composite series. PI_6FDA-APB(Si)_HBPI_{BPADA-TAP(Si)}-40%_SiO₂-20% has the largest storage modulus, 2952.0 MPa at 180 °C. The tan δ values of the composite films decreased from 0.96 to 0.73 with increasing HBPI_{BPADA-TAP(Si)} content. The ternary hybrid composites with densely cross-linked SiO₂ covalent networks developed in this study have improved dielectric, optical, thermal, and mechanical properties. Our fabrication method paves the way to the facile production of high-performance flexible and transparent electronic circuits that could be used in a broad range of applications in future electronics.