Abstract:5G mmWave, as a revolutionary cellular technology, holds monumental potential for innovations in many academic and industrial areas. However, widespread adoption of this technology is hindered by the severe overheating issues experienced by current Commercial Off-The-Shelf (COTS) mmWave smartphones. This study aims to identify the root causes of device skin temperature related throttling during 5G transmission, and to quantify power reduction required to prevent such throttling in a given ambient temperature. The key insight of our paper is leveraging the power model and thermal model of mmWave smartphone to acquire the quantitative relationship among power consumption, ambient temperature and device skin temperature. This approach allows us to determine the extent of power reduction required to prevent throttling under specific ambient temperature conditions.