To facilitate the fabrication of a reliable semiconductor package, the UV/heat dual curing of film adhesives was investigated. The curing system of the epoxy resin affected the film adhesive properties. As the UV/heat dual-curable epoxy resin, a modified o-cresol novolak epoxy resin, in which half of the glycidyl groups were substituted by acryloyl groups (OCN-AE), was applied to the film adhesive. The formulated film adhesive contained acrylic copolymer, OCN-AE, phenolic aralkyl resin as a heat-curing agent of the glycidyl groups, and 1-hydroxycyclohexyl phenyl ketone as a photoinitiator of the acryloyl groups. The formulated reference film adhesive contained unmodified o-cresol novolak epoxy resin (OCN-E) in place of OCN-AE. Formulated film adhesives containing a mixture of OCN-E and o-cresol novolak epoxy acrylate were also used as references. The morphology and the film adhesive properties were investigated. In these investigations, the film adhesive of OCN-AE showed better adhesive properties, lower modulus, and a better stress-relaxation ability than the referenced adhesives. As a result, a reliable film adhesive for semiconductor packages was successfully developed. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3466-3472, 2010