Electronic noise, despite being a limiting factor in many applications of semiconductor devices and integrated circuits, constitutes also a source of information about the microscopic processes taking place inside the devices. The level of noise and its frequency dependence can provide very useful knowledge about the dynamics of charge carriers, not available from the DC behavior. Monte Carlo simulations, performed precisely at a microscopic level, can be used to identify the link between the noise behavior of the devices and the peculiarities of carrier dynamics in high-frequency semiconductor devices. In this work we review several examples in which the noise performance of diodes and transistors contains information about some specific dynamics of electron and holes. In particular, we will deal with shot-noise suppression in ballistic and diffusive diodes, noise in Gunn diodes just before the onset of oscillations, plasmonic noise in FETs, kink-effect-related noise in HEMTs of different technologies and noise related to carriers injected at the gate of FETs.