Positron studies of defects in thin films and semiconductors are reviewed. The results obtained from experimental studies of Doppler broadening of annihilation radiation (DBAR) from variable energies are presented. Normalisation methods for the DBAR parameters S and W have been developed, allowing for direct comparisons of the results for different samples taken over long periods of time. The evaluation of the P:V parameter, the peak-to-valley ratio in a full annihilation spectrum, has been improved via a correction method that produced a fourfold increase in sensitivity to o-Ps annihilation. The spectrum ratio curve technique was improved and developed to investigate the chemical composition of the environment surrounding a positron-trapping defect. By fitting to multiple-element and/or defect-type responses the percentage of that particular element or defect contained within the sample could be found. Ratio curves were found to rely on the positron affinity to different vacancy types. Beam-based Doppler broadening spectroscopy, variable-energy positron annihilation spectroscopy (VEPAS), was used as a probe of oxide film and film/substrate interface characteristics. Different film growth methods were found to play a significant role in defining the features of films and their interfaces. Vacancies have a profound effect on the properties of semiconductor-type devices. A range of different structures and the effects of implantation have been investigated. VEPAS has been found to be useful in studying the more exotic types of materials, silica aerogel and niobium.