On the basis of papers published on the fundamental and excess LF noise sources in compound semiconductor transistors, two main issues are addressed in this paper: i) the characterization of LF noise sources linked to parasitic effects induced by innovative component architecture in emerging technologies such as GaN-based HEMTs and GaAsSb HBTs. ii) the identification of LF noise sources linked to degradation mechanisms in compound semiconductor devices issued from mature technologies. Examples of experimental correlation between LF noise and parasitic effects (i.e. potential electrical performance penalization) or failure mechanisms in III-V HEMTs and HBTs are described with data related to recent technological developments.