A fiber-containing resin substrate for collectively sealing a semiconductor devices mounting surface of a substrate having the semiconductor devices mounted thereon or a semiconductor devices forming surface of a wafer having semiconductor devices formed thereon, includes: a resin-impregnated fiber base material obtained by impregnating a fiber base material with a thermosetting resin and semi-curing or curing the thermosetting resin; and an uncured resin layer containing an uncured thermosetting resin and formed on one side of the resin-impregnated fiber base material. There can be a fiber-containing resin substrate that enables suppressing warp of a wafer and delamination of semiconductor devices even though a large-diameter wafer or a large-diameter substrate made of a metal and the like is sealed, enables collectively sealing a semiconductor devices mounting surface of the substrate or a semiconductor devices forming surface of the wafer, and has excellent heat resistance or moisture resistance after sealing.