This article provides a broad introduction to III–V semiconductors as a background to device and circuit technologies that use these materials. The reader is introduced to theoretical and practical concepts for this range of alloy semiconductors. The physical and chemical properties and behavior of these materials are discussed. Methods of growing epitaxial layers and fabricating microwave and RF devices are presented. A brief summary of the microwave applications of III–V semiconductors is included together with an overview of the state‐of‐the‐art performance.