PURPOSE: To improve moistureproof reliability, heat-resistant reliability and mechanical strength by conducting resin sealing by using a special resin composition containing a specific polymaleimido compound, a special polynuclear aromatic carboxylic acid allyl ester compound and a curing catalyst.

CONSTITUTION: A semiconductor element is resin-sealed by a resin composition comprising (A)-(C) components. (A) a maleimido compound having two or more of maleimido groups in one molecule. (B) a polynuclear aromatic carboxylic acid allyl ester compound of one or more of formulae I-III. (in formula, R represents phenylene or a 1-3C hydrocarbon group, at least one of R1-R5 -COO- CH2-CH=CH2 and others the 1-3C hydrocarbon group. (n) is 0 or 1.) (C) a curing catalyst. The resin composition is used for resin seal, thus reducing internal stress, then improving moistureproof reliability, heat-resistant reliability and mechanical strength.