The high coefficient of thermal expansion (CTE) of the epoxy composite frequently causes the CTEmismatch problem in semiconductor packaging. However, when the epoxy resins available currently are used for composite, the CTE-mismatch problem is inevitable even at the highly-filled conditions. In this study, the new type of bisphenol A (BPA) epoxy resin, i.e., ethoxysilyl-functionalized BPA epoxy was synthesized for the ultra-low CTE epoxy composite. The new epoxy composite with 85 wt% of silica content showed the ultra-low CTE of 3.2 ppm/degrees C and 6.0 ppm/degrees C at the temperature ranges of T < T-g and T > T-g, respectively. For comparison, the non-functionalized BPA epoxy composite was prepared under the similar conditions and it showed the CTE values of 8 ppm/degrees C and 40 ppm/degrees C at the temperature ranges of T < T-g and T > T-g, respectively. In order to understand the unique feature of the alkoxysilyl-functionalized epoxy, the reaction mechanism of the new epoxy was investigated using the model compound. (C) 2017 Elsevier Ltd. All rights reserved.