High-density horizontal InAs nanowire transistors are fabricated on the interdigital silicon-on-insulator substrate.Hexagonal InAs nanowires are uniformly grown between face-to-face (111) vertical sidewalls of neighboring Si fingers by metal-organic chemical vapor deposition.The density of InAs nanowires is high up to 32 per group of silicon fingers,namely an average of 4 nanowires per micrometer.The electrical characteristics with a higher on/off current ratio of 2 × 105 are obtained at room temperature.The silicon-based horizontal InAs nanowire transistors are very promising for future high-performance circuits.