The OPAL Microvertex Detector, installed in March 1993 at the CERN LEP collider, uses single sided 250 mum thick FOXFET biased detectors. Construction of the detector required systematic studies of detector properties in order to ascertain desirable characteristics of detectors used in the final construction. We present measurements based on a pool of more than 200 detectors, including properties such as visual quality, FET characteristics, and leakage currents.