A fiber-containing resin substrate includes a thermosetting epoxy resin-impregnated fiber base material, and an uncured resin layer formed on one side thereof formed from a composition containing: (A) a crystalline bisphenol A type epoxy resin and/or a crystalline bisphenol F type epoxy resin, (B) an epoxy resin that is non-fluid at 25° C. other than the component (A), (C) a phenol compound having two or more phenolic hydroxy groups in one molecule, (D) an inorganic filler, and (E) an urea-based curing accelerator. The fiber-containing resin substrate collectively encapsulates a semiconductor devices mounting surface or a semiconductor devices forming surface on a wafer level, even when a large-diameter wafer or a large-diameter substrate is encapsulated, to reduce warpage of the substrate or the wafer and peeling of a semiconductor device from the substrate, and to have the uncured resin layer excellent in storage stability and handleability before curing.