Presented in this thesis is a summary of the development of gallium arsenide position sensitive detectors. These are aimed at various applications with the original motivation being experimental particle physics. An account is given of basic semiconductor physics relevant to particle detectors. A review of electronics applicable to reading out charged signals from semiconductor detectors is included. Applications of gallium arsenide X-ray detectors are described together with results from a Monte-Carlo simulation of the spectrum obtained from an X-ray source. The design, fabrication and laboratory testing of detectors is presented for pixel and microstrip detectors and other test structures. Test beam results are also presneted for pixel and microstrip detectors. An introduction to ATLAS detector simulation is also given, with examples of detector descriptions for the GaAs Forward Semiconductor Tracker. Results from a generator level study of b-jets from the process Hbb and predictions of influences in the Forward Tracker are also given.