An integrated multireactor system for 2 x 2 parallel organic synthesis has been developed on a single glass microchip. Three-dimensional channel circuits in the chip were fabricated by laminating three glass plate layers. The fabrication method is a straightforward extension of the conventional one, and topological equivalence for any three-dimensional circuits can be constructed easily with it. 2 x 2 phase-transfer amide formation reactions, which constitute a simple model for combinatorial synthesis, were successfully carried out on the microchip, and the integrity of the three-dimensional circuits was confirmed. Combinatorial chemistry with multi-microreactors, in conjunction with a high-throughput screening method based on micro-TAS technologies, is expected to provide an efficient tool for drug discovery.