The chemical imaging sensor is a Si-based chemical sensor that visualizes the spatial distribution of a specific ion in the solution contacted with the sensing surface. It is based on the principle of the lightaddressable potentiometric sensor (LAPS), in which a modulated light beam is used to read out the ion concentration in the form of photocurrent. Since the conventional chemical imaging sensor uses a scanning light beam for mapping the distribution of the ion concentration, the long scan time has been a problem for imaging in real time. For high-speed imaging, a plurality of light beams modulated at different frequencies can be employed to measure the ion concentrations simultaneously at different locations. Although a wide frequency bandwidth is required for high-speed imaging, the modulation frequency is limited due to the low-pass characteristics of carrier diffusion in the conventional setup, in which the back-side of the Si substrate is illuminated. In this study, a high-speed chemical imaging system based on front-side-illuminated LAPS was developed, which achieved imaging of pH distribution at 70 frames per second.