This paper presents a case study research to analyze thermal performance of a type of Iranian underground living space, called Shavadan. Shavadan is part of building typology in the city of Dezful, southeast of Iran. The focus of the study is to introduce a passive design structure to further demonstration of the significance of the thermal performance analysis of Shavadan and the design effectiveness. Shavadan design structure, the main strategy of architects and building construction practitioners in the past, plays an important role to increase the indoor thermal comfort of buildings in hot and humid climates. Shavadans were built underneath houses, schools, mosques and public spaces at depths of 6–10 m, where the thermal behavior of the earth is almost stable. But this approach is totally forgotten in today’s buildings and people do not know how to use it, even if they desire to. Based on a measuring ambient air temperatures, in this paper the thermal behavior of five settings in different parts of Dezful is studied, from June to December. Moreover, the temperature stabilities of various Shavadans were compared to evaluate the architectural effectiveness of Shavadans in terms of the complex passive systems. The results show that it is useful to consider passive strategy as an auxiliary system to reduce domestic energy use in hot semi-humid climates where there is considerable electricity demand for air conditioning in the over 40°-Celsius-heat of these zones.