An ink supply port is opened in an Si substrate on which an ink discharge energy generating element is formed, by anisotropic etching, from a back surface opposite to a surface on which the ink discharge energy generating element is formed. When the anisotropic etching is effected, OSF (oxidation induced laminate defect) is remained on the back surface of the Si substrate with OSF density equal to or greater than 2.times.10.sup.4 parts/cm.sup.2 and a length of OSF equal to or greater than 2 .mu.m.