A method of producing a semiconductor device, comprising steps of 1) applying on a substrate a die bonding agent comprising a composition comprising an epoxy resin, an epoxy resin curing agent in such an amount that an equivalent ratio of a functional group of the epoxy resin curing agent to the epoxy group of the epoxy resin ranges from 0.8 to 1.25, thermoplastic resin particles which are solid at 25°C in an amount of from 3 to 60 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, and an epoxy resin curing promoter in an amount of from 0.1 to 10 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, wherein the composition, when analyzed by differential scanning calorimetry, shows at least one exothermic peak at a temperature lower than a temperature of an exothermic peak caused by curing of the epoxy resin, an apex temperature of said exothermic peak at the lower temperature being 80 °C or higher and lower than an apex temperature of the exothermic peak caused by the curing of the epoxy resin by at least 70°C, said DSC analysis being performed by heating an aluminum cell containing the composition and an empty aluminum cell as a reference at a temperature rise rate of 10°C/min from 25°C to 300°C in air, 2) heating the applied die bonding agent at a temperature of from T1 to (T2-20°C) to bring the die bonding agent to a B-stage, 3) placing a semiconductor element on the die bonding agent in the B-stage, and 4) curing the die bonding agent. 1) applying on a substrate a die bonding agent comprising a composition comprising an epoxy resin, an epoxy resin curing agent in such an amount that an equivalent ratio of a functional group of the epoxy resin curing agent to the epoxy group of the epoxy resin ranges from 0.8 to 1.25, thermoplastic resin particles which are solid at 25°C in an amount of from 3 to 60 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, and an epoxy resin curing promoter in an amount of from 0.1 to 10 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, wherein the composition, when analyzed by differential scanning calorimetry, shows at least one exothermic peak at a temperature lower than a temperature of an exothermic peak caused by curing of the epoxy resin, an apex temperature of said exothermic peak at the lower temperature being 80 °C or higher and lower than an apex temperature of the exothermic peak caused by the curing of the epoxy resin by at least 70°C, said DSC analysis being performed by heating an aluminum cell containing the composition and an empty aluminum cell as a reference at a temperature rise rate of 10°C/min from 25°C to 300°C in air, an epoxy resin, an epoxy resin curing agent in such an amount that an equivalent ratio of a functional group of the epoxy resin curing agent to the epoxy group of the epoxy resin ranges from 0.8 to 1.25, thermoplastic resin particles which are solid at 25°C in an amount of from 3 to 60 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, and an epoxy resin curing promoter in an amount of from 0.1 to 10 parts by weight per total 100 parts by weight of the epoxy resin and the epoxy resin curing agent, wherein the composition, when analyzed by differential scanning calorimetry, shows at least one exothermic peak at a temperature lower than a temperature of an exothermic peak caused by curing of the epoxy resin, an apex temperature of said exothermic peak at the lower temperature being 80 °C or higher and lower than an apex temperature of the exothermic peak caused by the curing of the epoxy resin by at least 70°C, said DSC analysis being performed by heating an aluminum cell containing the composition and an empty aluminum cell as a reference at a temperature rise rate of 10°C/min from 25°C to 300°C in air, 2) heating the applied die bonding agent at a temperature of from T1 to (T2-20°C) to bring the die bonding agent to a B-stage, 3) placing a semiconductor element on the die bonding agent in the B-stage, and 4) curing the die bonding agent.