© 2018 SPIE. Optical pump-terahertz probe spectroscopy is a powerful contact-free technique for probing the electronic properties of novel nanomaterials and their response to photoexcitation. This technique can measure charge carrier transport and dynamics with sub-picosecond temporal resolution. Electrical conductivity, charge carrier lifetimes, mobilities, dopant concentrations and surface recombination velocities can be measured with high accuracy and with considerably higher throughput than achievable with traditional contact-based techniques. We describe how terahertz spectroscopy is revealing the fascinating properties and guiding the development of a number of promising semiconductor materials, with particular emphasis on III-V semiconductor nanowires and devices.