A fiber-containing resin substrate for collectively encapsulating a semiconductor-device-mounting surface of a substrate on which semiconductor devices are mounted or a semiconductor-device-forming surface of a wafer on which a semiconductor device is formed, including a resin-impregnated fibrous base material which is obtained by impregnating a fibrous base material with a thermosetting resin and semi-curing or curing the thermosetting resin and has a linear expansion coefficient (ppm/° C.) in an X-Y direction of less than 3 ppm, and an uncured resin layer formed of an uncured thermosetting resin on one side of the resin-impregnated fibrous base material.