A novel thermocouple made of only a single metallic thin film is developed by S. Y. Xu and co-workers on page 3275. Its configuration challenges a long-lasting concept. By knitting a single-metal thermocouple (SMTC) into a matrix, one can easily make a SMTC array for 2D temperature mapping. As this extremely simple temperature sensor can also be applied to flexible substrates, it may inspire a new category of thermal sensors with versatile applications. This cover was designed by B. Xu and H. X. Liu.