Flexible and stretchable high-speed devices that operate at microwave level may enable wireless functionalities for many applications. The rise of flexible or stretchable electronic systems using inorganic semiconducting materials allow integration of high-performance electronic devices on foreign substrates, such as plastic or rubber. Here, we report on materials and design considerations for fabricating flexible and stretchable electronics systems that operate in the microwave level. High-speed active devices, including cost effective Si-based transistors and high-power GaN-based transistors, performing at multi-gigahertz frequencies are fabricated on either plastic or rubber substrates. Furthermore, important passive components, such as the capacitors, inductors and transmission lines that can together complete a microwave integrated circuit, are also demonstrated. All of the components presented here have comparable high-performances to their rigid counterparts, which can be combined to form microwave integrated circuits that can be used for many applications, where wireless functionalities are desired.