Ultrawide bandgap (UWBG) materials such as diamond, Ga2O3, BN and AlN, are a new class of semiconductors that possess a wide range of attractive properties, including very large bandgap, high critical electric field, high carrier mobility and chemical inertness. Due to these outstanding characteristics, UWBG materials are promising candidates to enable high-performance devices for RF and power electronics, ultraviolet photonics, quantum sensing and quantum computing applications. Despite their great potential, the research of UWBG semiconductors is still at a nascent stage and represents a challenging interdisciplinary research area of physics, materials science and devices engineering. In this talk, I will give an overview on the material properties, synthesis methods and device applications of UWBG semiconductors including diamond, Ga2O3, h-BN and AlN. I will also give a brief introduction of the invited speakers and their leading work in the field.