This paper presents a single-phase topology for multilevel inverters with minimum number of switching devices. The proposed topology significantly reduces the number of DC voltage sources, switches, and power diodes as the number of output voltage levels increases. The proposed multilevel inverter is constructed using series-connection of multilevel strings. Suggested multilevel string is composed of multiple basic switching units. The proposed multilevel inverter has extendable configuration that increases the number of output voltage levels more and more by adding more stages. The proposed multilevel inverter would be implemented in both symmetric and asymmetric configurations. Two different algorithms are introduced for determination of magnitude of DC voltage sources to reach the maximum number of output voltage levels with minimum number of semiconductor devices. Important characteristics of both symmetric and asymmetric configurations are extracted and compared with similar multilevel inverter topologies. Finally, a prototype of the proposed multilevel inverter is simulated and implemented experimentally to verify operation of the proposed multilevel inverter.