The first part of the thesis is an introduction to analog design integrated circuits in GaN. Different structures are presented, from the simplest ones such as current sinks, sources and mirrors, to more complex ones such as amplifiers, references and comparators. The second part of the thesis is a case study: during his internship period, the candidate was tasked with the design of an overcurrent protection system to be integrated in an already existing power stage project, in GaN. Different solutions were taken into consideration and the one that was deemed most suitable for the application, was extensively analysed, modelled and simulated.