Abstract: As the operating temperature of third-generation semiconductor devices increases, traditional epoxy molding compounds (EMC) with low glass transition temperatures (T_g) fail to meet the packaging requirements of high-temperature, high-power devices. To address this issue, this study has developed a cyanate ester-based epoxy molding compound with a glass transition temperature of up to 260℃ and subjected it to thermal aging tests at temperatures of 150℃, 175℃, and 200℃. The results showed that the storage modulus of the EMC significantly increased in the initial stage of aging, while the breakdown field strength remained above 40 kV/mm and the thermal decomposition temperature slightly decreased. After 15 days of aging, the storage modulus decreased by 12.8% and the breakdown field strength decreased by 15.2% under the condition of 200℃, but it was still higher than 35 kV/mm. The dielectric constant and the tangent of the dielectric loss angle were also at low levels. The thermal conductivity decreased sharply in the early stage of aging but the rate of decrease slowed down as the aging time extended. These results indicate that this epoxy molding compound exhibits excellent thermal stability and insulation properties under high-temperature aging conditions and has a broad application prospect.