Highly stable hydrophobic silica-based membranes were successfully fabricated through chemical post-modification of directly electrospun silica nanofibrous membranes. Five different Si-alkoxy chlorides were tried as reagents at room temperature, allowing for an easy two-step production process. Trimethylchlorosilane (TMCS) was determined as to be the most suitable modifier, for this purpose. The modified membrane exhibits long-term hydrophobicity even under high humidity and water submersion, maintaining this property after exposure to elevated temperatures and acidic conditions, surpassing the unmodified membrane. The separation effectiveness for immiscible water/solvent solutions was proven, followed by an investigation into the relation between the surface tension of some miscible water/solvent solutions and the resulting wetting behavior of the TMCS-modified membrane, to utilize the membrane as a process intensification tool, specifically as a solvent gate.