Patent ID: 8084530

Claim:
A sealing agent for an optical semiconductor device, which comprises: a silicone resin having a cyclic ether-containing group in the molecular structure; a heat curing agent capable of reacting with said cyclic ether-containing group; and a fine particulate material of silicon oxide, and the sealing agent having a viscosity of 500 to 10,000 mPa·s measured by an E-type viscometer at 25° C. at 5 rpm, a thixotropic value of 1.2 to 2.5 calculated by dividing a viscosity measured by the E-type viscometer at 25° C. at 1 rpm by a viscosity measured at 10 rpm (viscosity at 1 rpm/viscosity at 10 rpm), and a minimum viscosity of 100 mPa·s or higher measured at 1 s −1 in the temperature range of 25° C. to a curing temperature by a parallel plate rheometer.