The change of physical properties of an epoxy-molding compound (EMC) for semiconductor encapsulation according to the coupling treatment process change was investigated. Three different coupling treatment processes were applied in this study : the pretreatment method (PM), the internal pretreatment method (IPM), and the integral addition method (IAM). Especially, we suggested a simple and economic process, the IPM process, in which the drying and powdering process is excluded compared with the PM process. The optimum content range of the coupling agent is 1.0-2.0 wt % based on the weight of the filler, which is about a 1.3-2.5 coating layer. The flexural strength and internal stress of EMC made by the IPM process is almost equivalent to that made by the PM. We applied the model of complex layers of a silane coupling agent at the filler/matrix interface in interpretating the mechanical and thermal properties of EMC and obtaining the relationships between physical properties and the coupling process. It can be concluded that the IPM process is an effective and economic process to be able to obtain a good reliable EMC with strong mechanical strength and low internal stress.