PURPOSE: To make the moistureproofness of an epoxy resin composition excellent and to prevent the deterioration of the reliability of the epoxy resin composition after a soldering treatment by a method wherein, in the epoxy resin composition for semiconductor-sealing, the specific amount of ureidosilane and the specific amount of mercaptosilane are used jointly in a specific mixture ratio.

CONSTITUTION: In a resin composition which is composed mainly of an epoxy resin, a phenol novolak resin, a hardening promoter and an inorganic filler, 0.1 to 2.0wt.% of ureidosilane A and 0.1 to 2.0wt.% of mercaptosilane B are contained. When both are used jointly in a mixture ratio of A/B=1.0 to 10.0, the reliability of the composition is enhanced by leaps and bounds and its level becomes good when the composition is pasted to be thin. When the ratio of A/B is less than 1.0, the reliability is lowered. When the ratio of A/B exceeds 10.0, the molding working property and the reliability of the composition are worsened and not favarable. A semiconductor package sealed by using the composition is mounted on a circuit board; it is immersed in a soldering tank. Even after that, it is possible to obtain the package whose moistureproofness is excellent and whose reliability is high. The package has a feature that its burr is small in a molding operation.