It has long been acknowledged that TCP performance suffers in hybrid networks. A Split TCP approach has been proposed to address this problem. In this approach, a proxy is employed at the boundary of wired networks (e.g. the Internet) and wireless networks (e.g. Cellular #etworks, WLan or Mobile Ad Hoc #etworks). This strategy significantly improves TCP performance. However, it does not maintain the end-to-end semantics of TCP. The loss of end-to-end semantics may cause problems to applications that rely on such a guarantee provided by TCP. In this paper, we introduce a novel technique called Semi-Split TCP to address the problem without sacrificing the benefits of Split TCP. We present the architecture and algorithms of the proposed technique; and give implementation, simulation, and analytical results to illustrate the feasibility of this method. Our simulation results demonstrate that Semi-Split TCP can achieve similar performance as Split-TCP without sacrificing the end-to-end semantics.