GaAs on Si3N4 bonded wafers are a type of compound semiconductor wafer where a layer of gallium arsenide (GaAs) is bonded to a layer of silicon nitride (Si3N4). This type of wafer is used in a variety of applications, including high-frequency and high-power devices such as RF amplifiers, microwave transistors, and solar cells. The use of Si3N4 as a bonding layer allows for better thermal management and improved electrical performance compared to traditional GaAs substrates.