A collaborative project between the Surrey Ion Beam Centre and the positron beam group at the University of Bath is developing a bench-top positron tool suitable for use in the semiconductor industry. The technique's non-destructive nature, coupled with its high sensitivity to defects, makes it a potentially ideal method for detecting process problems at an early stage. Measurements on the existing laboratory-based system have shown, for example, a high sensitivity to variations in parameters such as temperature in the growth of epitaxial layers. An instrument suitable for use in the fabrication environment is described, together with diagnostic studies of PECVD-deposited SiN layers, of thicknesses in the range 21–133 nm, performed in conjunction with ellipsometric and RBS measurements. The technique is sensitive to the atomic composition of the SiN epilayers and, in conjunction with ellipsometry, is able to measure the density of the layers and to quantify the densification on annealing at 900°C.