Solar-driven chemical conversion using photoelectrochemical (PEC) cells has attracted intense interests to produce value-added chemical fuels and feedstock using solar energy. In particular, silicon is attractive for a photoelectrode since it’s earth-abundant and low cost, and has small bandgap to absorb most of solar spectrum. However, silicon suffers from slow kinetics for PEC reactions such as water splitting and CO₂ reduction and also from severe corrosion during the operation. In this talk, I’ll present our strategies to develop a high performance and stable silicon-based PEC cells. Firstly, I’ll discuss the light-matter-chemical interaction occurring on a photoelectrode’s surface and demonstrate that PEC reactions are coupled with light abosorption and electrocatalysis bound on the surface of a photoelectrode. Based on these understanding, I’ll present our approaches to maximize light absorption and electrocatalysis in PEC cells (1) by using locally defined 3-dimensional cocatalysts and (2) by using a transparent cocatalysts on Si photoelectrodes. Influences of surface area and coverage of cocatalysts as well as charge transport properties of Si photoelectrodes will be presented using water oxidation reaction as a model chemical reaction. I’ll also show that these approaches can be applicable to CO₂ reduction reactions.