Three-dimensionally structured semiconductors, such as nano and microwire arrays, enable orthogonalization of light absorption and carrier collection in photovoltaics and fuel-producing photoelectrochemical cells – potentially allowing the use of relatively low-purity semiconductors in relatively high-efficiency solar-energy-conversion devices. In this colloquium I will first describe work completed during my postdoctoral studies at Caltech with Nate Lewis and Harry Atwater including: (1) the growth of high-quality Si wires with controllable p-type doping and the evaluation of their solar energy-conversion performance using a test electrolyte that forms a rectifying conformal semiconductor-liquid contact, (2) the fabrication and characterization of solid-state Si radial pn junctions based on this wire array platform, (3) the integration of these arrays with hydrogen-evolving catalyst particles in order to directly drive the hydrogen-producing half reaction associated with water photoelectrolysis, and (4) the characterization of enhanced optical absorption in wire-array devices. I will end with a brief presentation of our nascent efforts at the University of Oregon to synthesize and study stable, structured semiconductors and electrocatalysts for driving the oxygen-evolving half-reaction associated with water splitting and other photoelectrochemical solar-fuel-generation schemes. Dr. Boettcher is a Signature ONAMI Research at the Department of Chemistry, University of Oregon.