A facile method for preparing highly conductive hybrid organic-inorganic membranes is reported. These membranes are synthesized using an electrospinning process with a sol-gel-based solution containing PVDF-HFP (polyvinylidenefluoride-hexafluoropropylene), functionalized or not functionalized silicon alkoxides, and additives. Proton conduction measurements highlight that these hybrid membranes exhibit conductivity value of 101 mS/cm at 120 degrees C under 80% RH (relative humidity), comparable to the best Nafion measured under the same conditions. These membranes have a proton conductivity-humidity variation close to Nafion and a modulus value higher than that for Nafion above 80 degrees C. Their proton conductivity value is about 15 mS/cm under 50% RH, and it constitutes one of the highest values reported. These interesting properties are related to the microstructure of the electrospun membranes that have been characterized using field emission scanning electron microscopy (FE-SEM) and small angle neutron scattering (SANS). The electrospun membranes are made composed of a bundle of fibers surrounded by a functionalized silica network. The bundle of fibers corresponds to the assembly of small polymer fibers surrounded by small anisotropic functionalized silica domains. Coupling the reactive chemistry of the sol-gel-based process with electrospinning allows the design of hybrid membranes with fractal hydrophobic/hydrophilic interfaces exhibiting different length scales.