Defects of components as a result of entrapped gases during an injection process could be minimized with the utilization of a gas-permeable metal die material in the mold, due to its excellent permeability of air. Conventional gas-permeable die materials employ low temperature sintering of loosely packed steel powders with or without the addition of pore-forming polymers, whose microstructures are usually weak and their gas permeability values are also low. In this study, gas-permeable metal die materials are developed using tool steel powder, packed in a mold having the insertion of orthogonally arrayed polymer wires. Linear gas-permeable channels in orthogonal array are thus developed by the burning out of the polymer wires, which yield a large value of air permeability. The value of air permeability can be adjusted by changing the diameter and number density of the polymer wires. The tool steel powder can be made fully dense by supersolidus liquid phase sintering, yielding a microstructure with a wear resistance value much larger than that of the conventional gas-permeable die material.