A method for manufacturing a substrate material for a semiconductor package, including a step of increasing a temperature of a laminated body in which a metal foil, one or more prepregs, and a metal foil are laminated in this order to a hot-press temperature while pressurizing the laminated body. The prepreg contains an inorganic fiber base material and a thermosetting resin composition. A content of the thermosetting resin composition is 40 to 80% by mass on the basis of a mass of the prepreg. In the step of increasing the temperature of the laminated body to the hot-press temperature while pressurizing the laminated body, the laminated body is heated in a condition in which the lowest melt viscosity of the prepreg is 5000 Pa·s or less.