Optical transceiver modules are commonly used in telecommunication and data communications systems. These modules, which are located in the optical I/O ports at the front-end of switches and routers, are a dominating source of electromagnetic interference (EMI) problems at their operation frequency and/or harmonics. In this study, a simulation model is used to investigate the EMI coupling physics and performance of the silicon optical sub-assembly (OSA) module. Total radiation power (TRP) measurement has also been performed in a mode-stirred reverberation chamber (RC) to support the radiation mechanism analysis. The connector between the module circuit board to flex cable has been identified as the major EMI source above 15 GHz in the OSA module. This conclusion can help provide insight to EMC design engineers about the potential EMI problems in the OSA package.