This paper presents a new approach based on Benders decomposition (BD) to solve short-term hydrothermal coordination problem with AC power flow, voltage stability and security constraints. The proposed method decomposes the problem into a master problem and a sub-problem. The master problem applies the Mixed Integer Programming (MIP) method and finds the on/off states of the thermal and hydro units and the amount of power produced by each hydro unit. The sub-problem apply the nonlinear Programming (NLP) method and find the amount of power produced by each thermal unit while modeling the transmission network using AC power flow considering security and voltage stability constraints. Index evaluates voltage stability of the power system. Due to AC power flow and security constraints, the sub-problem may become infeasible. To cope with the infeasibility problem, positive penalty terms are added to the sub-problem formulation.The methodology is tested on the 9-bus and IEEE 118-bus test systems. The obtained results confirm the validity of the developed approach.