In highly dense tropical cities, a semi-outdoor space (SOS) is frequently used as a social space within tall building forms where people can interact and connect. Thermal comfort in SOSs within tall buildings, however, may vary depending on the type and form attributes that define it. This study classifies 63 SOSs in four tall buildings of Singapore into five types based on literature review: perimeter buffers, sky terraces, horizontal breezeways, breezeway atria and vertical breezeways. Findings suggest that the five SOS types perform differently in terms of thermal comfort (based on PMV*), environmental parameters (air temperature, mean radiant temperature, relative humidity, and air velocity), and building form attributes (height-to-depth ratio, open space ratio, and green plot ratio). Of these five, vertical breezeways and horizontal breezeways are the most thermally comfortable for all activities during a typically warm hour. It is postulated that higher thermal comfort levels in these SOS types are linked to form attributes that enhance air velocity. This study examines the pros and cons of each SOS type in terms of thermal comfort in their role as communal spaces in tall buildings situated within a highly dense tropical city.