<p>Conformal integration of electronics with soft, irregular organ topologies remains challenging, as tissue-like platforms with bulky dimensions ranging from a few millimetres to several hundred micrometres result in incomplete signal acquisition and chronic tissue compression. Although ultrathin nanoscale devices have recently been developed to address these challenges, they involve complex and delicate handling processes that limit their practical use and compromise their intrinsic performance. Here we present the development of a transformable and imperceptible hydrogel–elastomer adhesive bilayer based on ionic–electronic conductive nanomembranes (THIN) with a thickness of 350 nm. This approach leverages the amphiphilic properties and the combination of a hydrophilic tissue-adhesive hydrogel and a hydrophobic semiconducting elastomer. Dynamic bonding interactions at a heterogeneous interface, formed through a spin-coating process using orthogonal solvents, facilitate full compatibility with microfabrication. THIN exhibits an instantaneous rigid-to-soft phase transformation, transitioning from a hardness of 1.35 to 0.035 GPa and a stiffness of 0.16 to 9.08 × 10⁻⁵GPa μm⁴, enabling facile handling when dried. On hydration, THIN achieves complete conformal contact with diverse surfaces, including those with low bending radii, along with rapid spontaneous adhesiveness. To demonstrate the unique electrical and mechanical characteristics, THIN was integrated into the active channel of an organic electrochemical transistor with a high <i>µC*</i> (<i>µ</i>, charge-carrier mobility; <i>C*</i>, volumetric capacitance). The resulting THIN-OECT exhibited an exceptional strain-insensitive ion–electron conduction performance, facilitating imperceptible tissue interfacing and precise biosignal monitoring through transformable phase changes.</p>