A field effect chemically sensing device, suited for the generation of scanning light pulse technique (SLPT) chemical images, was proposed. The device was a MOS capacitor made on p-Si (10 ?), thermally oxidized to 120 nm and metallized on its underside with 200 nm of Al. The biasing electrodes were two parallel Al tracks 100 nm thick spaced 1 mm from each other. The results demonstrate the complete separation between biasing and sensing functions in devices designed for SLPT chemical image generation.