A liquid-discharging-head substrate includes an insulation layer, an electrode, and a heating resistor element, wherein the insulation layer includes a first opening portion including a first opening formed in a surface of the insulation layer, a second opening having a smaller opening area than an opening area of the first opening, and a surface connecting the first opening and the second opening, and a second opening portion extending from the second opening to a back surface of the insulation layer, wherein the electrode is formed in the second opening portion, and a surface of the electrode is exposed from the second opening when viewed from the surface side of the insulation layer, and wherein the heating resistor element is in contact with the surface connecting the first opening and the second opening, and with the surface of the electrode.