We developed a fabrication process of narrow-gapped twin nano-tips for atomic force microscopy (AFM) dual probes. A tetrahedral dual tip consisting of an inclined crystalline Si (111) plane and two dry-etched vertical planes was fabricated using deep reactive ion etching (D-RIE) to form a (110)-oriented narrow trench, thermal oxidation and additively refilling the trench with resin to protect the sidewalls, mechanically polishing-back the top resin and SiO₂ layers to expose the Si (100) surface, and anisotropically etching the crystalline Si to form the (111) plane. The mechanically polished SiO₂ thin film and resin layer were used to protect the trench sidewalls thereby preventing the gap between the Si tips from widening because of oxidation. A dual tip with a 450 nm gap was obtained by using the fabrication process. In addition to protecting the Si sidewalls with a SiO₂ thin film, the resin refilling prevented abrasive particles from penetrating into the trench.