An encapsulating resin composition for a power device comprising: an epoxy resin; an inorganic filler; a curing agent; and a curing accelerator, wherein the inorganic filler contains a surface-treated silica which is modified with a coupling agent, and wherein the encapsulating resin composition is molded under a condition of 175°C for 2 minutes and then subjected to after-curing under a condition of 175°C for 4 hours to obtain a test piece having a diameter of 100 mm and a thickness of 2 mm, and a half width of a current-time curve obtained by measuring the test piece with a thermally stimulated depolarization current method according to an order of (i) to (v) below is equal to or less than 800 seconds, (i) a temperature of the test piece is increased to 150°C at a rate of 5°C/min without applying a voltage, (ii) a constant voltage of 500 V is applied for 30 minutes while maintaining the temperature of the test piece at 150°C, (iii) the temperature of the test piece is lowered to 45°C at a rate of 5°C/min while applying the constant voltage of 500 V, (iv) the application of the voltage is stopped while maintaining the temperature of the test piece at 45°C and the test piece is left to stand for 5 minutes, and (v) the temperature of the test piece is increased at a rate of 3.5°C/min without applying any voltage to the test piece, and a value of a current flowing during the increase in the temperature is measured to obtain a current-time curve. an epoxy resin; an inorganic filler; a curing agent; and a curing accelerator, wherein the inorganic filler contains a surface-treated silica which is modified with a coupling agent, and wherein the encapsulating resin composition is molded under a condition of 175°C for 2 minutes and then subjected to after-curing under a condition of 175°C for 4 hours to obtain a test piece having a diameter of 100 mm and a thickness of 2 mm, and a half width of a current-time curve obtained by measuring the test piece with a thermally stimulated depolarization current method according to an order of (i) to (v) below is equal to or less than 800 seconds, (i) a temperature of the test piece is increased to 150°C at a rate of 5°C/min without applying a voltage, (ii) a constant voltage of 500 V is applied for 30 minutes while maintaining the temperature of the test piece at 150°C, (iii) the temperature of the test piece is lowered to 45°C at a rate of 5°C/min while applying the constant voltage of 500 V, (iv) the application of the voltage is stopped while maintaining the temperature of the test piece at 45°C and the test piece is left to stand for 5 minutes, and (v) the temperature of the test piece is increased at a rate of 3.5°C/min without applying any voltage to the test piece, and a value of a current flowing during the increase in the temperature is measured to obtain a current-time curve. (i) a temperature of the test piece is increased to 150°C at a rate of 5°C/min without applying a voltage, (ii) a constant voltage of 500 V is applied for 30 minutes while maintaining the temperature of the test piece at 150°C, (iii) the temperature of the test piece is lowered to 45°C at a rate of 5°C/min while applying the constant voltage of 500 V, (iv) the application of the voltage is stopped while maintaining the temperature of the test piece at 45°C and the test piece is left to stand for 5 minutes, and (v) the temperature of the test piece is increased at a rate of 3.5°C/min without applying any voltage to the test piece, and a value of a current flowing during the increase in the temperature is measured to obtain a current-time curve.