The research reported is concerned with the modelling of VHF power transistors in the context of power amplifier and frequency multiplier application. A large signal model is required, capable of representing the device under switching conditions with the collector entering saturation. Particular interest is in amplifiers and multipliers where the collector is switched into and out of forward injection, spending a brief period in the saturation state. The type of device studied is of multi-emitter structure, with a wide collector epitaxial region. It is believed that extrinsic charge storage in the base region and in the collector dominate the behaviour of the collector junction when operating under forward injection conditions. An intuitive approach to modelling is adopted, in which the device is divided into major regions and each is represented by the simplest lumped model that appears feasible. Experimental work has been concerned with the study of the switching response of the device, attempts at charge control characterization and deduction of the form of the model necessary to represent effects associated with the collector junction.