In regions with hot climate, most office buildings tend to use mechanical cooling for indoor thermal comfort, which results in high energy consumption throughout the year. In this article, we highlight a case study in an office building in Shenzhen, which is located in the Hot Summer and Warm Winter Zone of China. The building's most distinctive feature is that it makes sufficient use of semi-outdoor spaces, which plays an important role to achieve occupants' comfort, meanwhile contribute to saving energy. Field studies were conducted on an open terrace and in an auditorium with openable walls. Air temperature on the open terrace varied between 28.8℃ and 30.6℃ during working hours on a summer day. Most occupants felt comfortable, although their averaged thermal sensation vote tended to be higher than neutral condition. In the auditorium when it was occupied on an autumn day, air temperature ranged from 26.1℃ to 27.4℃. The averaged thermal sensation vote values in the three sitting areas were −0.5, 0.3, −0.2 respectively, while no less than 70% of people felt thermally comfortable. In both spaces, the sensible airflow had positively impacted on occupants' comfort. The case study has proven the effectiveness of the strategy of using semi-outdoor spaces and could be a grounded example for new building designs in hot regions in China.