Hot planets or planets having harsh environments (e.g. Mercury and Venus) are abundant in the solar system. Specifically, Venus is a hot planet with a world similar to earth and exploring how climate and geology work on Venus could potentially provide a deeper understanding of the processes at work in our own environment. As such, there is an increasing interest in exploring such hot planets; but so far, the missions to these extreme environments have been very limited in scope and duration mainly due to unavailability of sensors and readout electronics that can survive the extreme environments of the planet . Recently, researchers have developed robust electronic devices and circuits that are resilient under the harsh space conditions. For example, ceramic semiconductor materials, such as gallium nitride (GaN) and silicon carbide (SiC) have been used to create space-grade microelectronics taking advantage of their temperature-tolerance, radiation-hardness and chemical stability. In the GaN material family, research into AlGaN/GaN heterostructures with high temperature capabilities has been ongoing for several decades. More recently, researches have shown that InAlN/GaN devices are operational up to 1000°C in vacuum. While there are compelling reports on the operation of electronics and circuits that sustain high temperature operation, there has not been much effort in developing sensors that can support scientific missions to hot planets. In this talk, I will go over new sensors and microsystems in GaN that can be monolithically integrated with either InAlN/GaN or AlGaN/GaN electronics to take various measurements including infrared, magnetic, and seismic, and thus enable long-lasting missions to hot planets with unprecedented science return.