This letter proposes a converter-level method for measuring the on-state voltages of all power semiconductors in a single-phase inverter by using a single circuit only. The proposed circuit distinguishes itself by connecting to the middle-point of each phase-leg, instead of the two power-terminals of individual devices as conventional methods do. It has the advantages of reduced circuit complexity, size, cost, and ease of connection. The principle and theoretical analysis of the proposed converter-level method are discussed. A case study on a single-phase full-bridge inverter is demonstrated to prove the concept.