Solar energy conversion is spotlighted as a technology to address environmental and energy problems. Among various technologies, photocatalytic water splitting to produce hydrogen and oxygen using a semiconductor-based material has received great attention. Moreover, when the plasmonic metal nanostructure is incorporated into the semiconductor, the photocatalytic efficiency can be enhanced through the transfer of plasmonic energy from the plasmonic metal to the semiconductor. Our group explores enhanced photocatalytic activity by implementing effective plasmonic energy transfer through rational design of metal-semiconductor composites.