A liquid ejection head substrate including a silicon substrate having a liquid supply port as hollow and slots as through holes connecting the hollow and a liquid channel arranged opposite sides of the substrate. The method includes etching the substrate to form the hollow; forming a first resist on the hollow; etching the first resist on the bottom of the hollow under conditions of securing an equal etching rate to both the silicon substrate and the first resist; forming a second resist on the hollow; patterning the second resist into an etching mask; and etching the substrate using the etching mask to form the through holes.