AbstractBy virtue of their narrow emission bands, near‐unity quantum yield, and low fabrication cost, metal halide perovskites hold great promise in numerous aspects of optoelectronic applications, including solid‐state lighting, lasing, and displays. Despite such promise, the poor temperature tolerance and suboptimal quantum yield of the existing metal halide perovskites in their solid state have severely limited their practical applications. Here, a straightforward heterogeneous interfacial method to develop superior thermotolerant and highly emissive solid‐state metal halide perovskites is reported and their use as long‐lasting high‐temperature and high‐input‐power durable solid‐state light‐emitting diodes is illustrated. It is found that the resultant materials can well maintain their superior quantum efficiency after heating at a temperature over 150 °C for up to 22 h. A white light‐emitting diode (w‐LED) constructed from the metal halide perovskite solid exhibits superior temperature sustainable lifetime over 1100 h. The w‐LED also displays a highly durable high‐power‐driving capability, and its working current can go up to 300 mA. It is believed that such highly thermotolerant metal halide perovskites will unleash the possibility of a wide variety of high‐power and high‐temperature solid‐state lighting, lasing, and display devices that have been limited by existing methods.