Abstarct: State estimation plays an important role in ensuring reliable and safe operation of power systems. As the complexity and size of modern power grids increase, accurate estimation of system state variables becomes challenging. Hierarchical multi-area state estimation is a technique used in power systems to estimate the states of several interconnected areas. The key advantage of hierarchical multi-area state estimation is its ability to estimate the state of a large system in a decentralized manner with less computational complexity. Considering inter-regional correlations also provides a more comprehensive picture of the power system's behavior and enables operators to make informed and better decisions. This thesis presents a high-speed method for hierarchical multi-area state estimation. The proposed method consists of two steps. In the first step, linear and one-step state estimation is performed for each area baxsed on SCADA measurements. In the second stage, the coordinator takes on the task of estimating the slack angle of each area and, in other words, coordinating the voltage angles of the entire system. This coordination relies on data sent regarding the voltage magnitudes and angles of the boundary buses from the areas, as well as the active and reactive powers of the tie lines. The proposed method is implemented on the IEEE 118-bus network using MATLAB software. The simulation results indicate the optimal performance of the proposed method, which offers advantages such as higher speed and freedom from convergence concerns compared to conventional iteration-baxsed methods.