Although the tropopause is a well‐established concept, its definition and physical properties remain an active research topic. In the tropics, both the World Meteorological Organization established lapse rate tropopause definition and the minimum in the temperature profile (the cold point) are used to determine the tropopause height. We examine the differences produced by these two definitions using high‐resolution airborne in situ measurements of temperature, water vapor, and ozone in the tropical tropopause layer from a recent experiment over the western Pacific using the National Aeronautics and Space Administration (NASA) Global Hawk unmanned aircraft system. When the two definitions do not produce the same tropopause height, which is in about half of the cases, the combined temperature and trace gas analysis shows that the lapse rate definition better identifies the transition from the troposphere to the stratosphere. Plain Language Summary Discovered more than a century ago, the tropopause is known to mark the boundary of two dynamically and chemically distinct layers of atmosphere, the stratosphere, and the troposphere. In the tropics, the location, temperature, and physical/chemical gradients of the tropopause are important as part of the fundamental knowledge of the atmosphere and for regulating the amount of water vapor entering the stratosphere, which has a significant contribution to climate forcing. The tropopause over the tropical western Pacific, in particular, is known as the decisive region for determining the amount of stratospheric water vapor. High‐resolution measurements for this region are rare because the region is remote and tropopause altitudes are difficult to access. An airborne experiment targeting this decisive region was conducted in 2014, using the National Aeronautics and Space Administration (NASA) Global Hawk unmanned aircraft system. These high‐resolution temperature and trace gas data provided an unprecedented opportunity to examine the physical meaning of the two tropical tropopause definitions, known as the lapse‐rate tropopause and the cold‐point tropopause. In this work, we demonstrate how the relationship of two chemical tracers, ozone and water vapor, can unambiguously identify the transition from troposphere to stratosphere and therefore serve to diagnose the effectiveness of the different tropopause definitions. Key Points The tropical tropopause definitions are examined using airborne in situ measurements over the tropical western Pacific O3 and H2O relationship is used to identify the air mass change from the troposphere to the stratosphere The lapse rate definition is shown to more consistently identify the tropopause based on the tracer diagnostic