Southeast Asia has seen rapid urban growth over the past 20 years, leading to rising city temperatures. This study explores how these temperature changes are linked to urban development and changes in land use across 19 cities of different sizes, from megacities to small cities. Results demonstrate that larger cities show more intense and widespread LST augmentations extending into rural areas. Megacities experience significant LST growth near urban centers despite limited built-up expansion. Some areas in many cities got cooler over time due to the expansion of vegetation cover. Unlike other regions, vegetation plays a vital role in effectively moderating urban heat in Southeast Asian cities. This study provides actionable evidence for balancing development with enhancing green spaces, redirecting growth to smaller cities, and shifting development from city centers to urban outskirts.