New chemical vapor deposition (CVD) processes controlled by light irradiation have been studied and applied to device processing. The physical interaction between the photons of the incident. light and the gas-semi-conductor system are either photolytic or pyrolytic. Lamps or lasers can be used in both processes respectively for large area thin film deposition or thin film direct writing. The control of the reaction by the light implies that the thermal exposure of the substrate is minimized. Light assisted CVD is thus a cold process suitable for brittle materials such as III-V compound semiconductors and also suitable for in-situ multi-processing. Exemples of dielectric layer formation will be treated with emphasis on electronics properties as a warrant of material and interface quality. In situ multiprocessing is also illustrated here.