In this paper, lateral effect position-sensitive detectors based on the MOS principle have been fabricated in lengths of 15 mm, 45 mm and 60 mm. The gate contact covering the active area consists of indium tin oxide which is a degenerate semiconductor transparent in the visible spectral range. Characterization and analysis have both been performed especially withparticular focus on the nonlinearity believed to be caused by stray stress induced in the inversion channel originating in the indium tin oxide gate contact. Stress in the channel will change the resistance in a non-uniform manner because of the piezoresistance effect, thus causing a nonlinearity in the position determination. It has been shown that the heat treatmentgreatly influences the linearity of the position-sensitive detectors. A heat treatment performed correctly results in 60 mm and 15 mm detectors with nonlinearity within ±0.1% and 45 mm detectors with nonlinearity within ±0.15% over 60% of the active length. This is an improvement over the previous results with this type of MOS position-sensitive detector. By performing a correctly timed heat treatment this PSD type has the potential to be used incommon position-sensing applications.