The invention provides a curable resin composition containing (A) a multifunctional benzoxazine compound having at least two benzoxazine rings, the compound being at least one multifunctional benzoxazine compound selected from a multifunctional benzoxazine compound having a structural unit of formula (1) and a multifunctional benzoxazine compound represented by a structure of formula (2), (B) a multifunctional epoxy compound having at least one norbornane structure and at least two epoxy groups, (C) a curing agent, and (D) a curing accelerator which is a bisphenol salt of a diazabicycloalkene. The invention also provides a cured product of the curable resin composition and methods of producing the curable resin composition and the cured product, as well as a semiconductor device using the cured product as a sealant.