Envelope tracking (ET) is a key technology to improve the efficiency of RF Power Amplifiers (PA). ET has been widely adopted in the last decade but it suffers from efficiency degradation when moving to Beyond 5G applications because of the increased signal bandwidth. Objective of the proposed thesis is to propose an innovative ET-PA system with high efficiency and wideband characteristics taking benefit of CMOS-GaN hybrid integration schemes in order to propose high efficiency, yet compact, ET-PA solutions for Beyond 5G applications. The PhD student will explore different ET Modulator (ETM) architectures. He/she will be in charge of the specification of the different ETM sub-blocks and will carry out the design at transistor level. The proposed circuits will be co-integrated with the PA solutions developed by CEA-Leti researchers and will be manufactured. The PhD student will then design test boards, perform electrical characterization of the circuits and implement a demonstrator to experimentally validate the proposed solution. The thesis will follow an iterative learning scheme, the number of iterations depending on the progress of the candidate over the three years, the fabrication of the circuits, and the evolution of the electrical specifications. The PhD student will develop skills in Power Management, Analog and RFIC PA design.