A new concept for a 3D microstructured photocatalyst for hydrogen production by water-splitting under direct sunlight is proposed. The optimization process of deep-reactive ion etching process and the subsequent deposition of TiO2 thin films by physical vapor deposition decorated with Au nanoparticles allows H2 production by direct water splitting. The influence of the area enlargement factor on the 3D photocatalyst surface morphology and its photocatalytic performance under UV-visible irradiation was thoroughly analyzed and corroborated by electrochemical experiments. The photocatalyst exhibited an increase in H2 production by almost a factor of 12 compared to conventional planar TiO2 films.