Provided is an encapsulant resin for a semiconductor that effectively functions even with a relatively small amount of an additive. The encapsulant resin for a semiconductor is characterized in that the additive has a concentration gradient in the direction of thickness of the encapsulant resin. Specifically, the concentration gradient of the additive is established in the direction of thickness of the encapsulant resin by stacking at least two types of organic polymer resins containing different contents of the additive to form the encapsulant resin or by applying an electric field to the encapsulant resin to effect electrophoresis of the polar additive in the encapsulant resin.