With the rapid load increase in some countries such as China, power grids are becoming more strongly interconnected, and the differences between peak and valley loads are also increasing. As a result, some bulk power systems are facing high voltage limit violations during light-load periods. This paper proposes to utilize transmission switching (TS) to eliminate voltage violations. The TS problem is formed as a mixed-integer non-linear program (MINLP) with AC power flow constraints and binary variables. The proposed MINLP problem is non-deterministic polynomial hard. To efficiently solve the problem, a decomposition approach is developed. This approach decomposes the original problem into a mixed integer linear programming master problem and an AC optimal power flow slave problem that is used to check the AC feasibility. Prevention of islanding is also taken into consideration to ensure the feasibility of the TS results. The modified IEEE 39-bus and IEEE 57-bus test systems are used to demonstrate the applicability and effectiveness of the proposed method.