Provision of adequate electricity is one of the major factors for industrial and commercial development. However, decisions on the expansion of electricity are bogged down by high investment requirements and nonsynchronized expansion between electricity generation and transmission systems. As a rule, the investment requirements for these types of projects are immediate but their benefits can be obtained only in the long-term basis albeit electricity planners base their decisions on immediate requirements of shorter terms. As investment funds are very hard to come by, the funds, if available, should be utilized to maximum by minimizing the investment through a synchronized expansion planning of both electricity generation and transmission systems. This paper attempts to address this opportunity. We have proposed here a mixed integer model to develop concurrent transmission and generation investments plans. The model selects new generation plants or generation capacity expansions for existing plants that are located on the interconnected network by considering explicitly congestion in the transmission network. Hence the model contributes to this area by filling in the gap between models for developing long-term power generation policies and power flow models focusing on transmission network expansion. The application of the model in Turkey's electricity network highlights the country's congested areas in the transmission network, which might lead to loss of load and inefficient generation capacity expansion if not tackled properly. The analysis shows that a cost efficient generation expansion is possible to realize in congested regions if proper transmission expansion decisions are made concurrently with generation expansion decisions.