Semiconductor core fibres represent an emerging technology with potential applications in many areas, including photovoltaics and optical transmission. Recent advances in fibre manufacturing techniques has allowed long, continuous silicon core fibres to be produced in commercial draw towers. The effect of the molten core fibre fabrication method on the electrical properties of silicon cores from glass-clad fibres have been studied. Fibres with core diameters ranging from 60 to 300 µm were produced using a CaO interface modifier between the core and cladding. Five silicon material types with increasing phosphorus doping levels were analysed before and after the drawing process using four point probe technique, supplemented with microscopy and compositional analysis. Novel techniques for preparing and measuring fibre samples were developed, which is suitable for a range of fibre diameters. Cores produced from lightly doped materials showed a large increase in conductivity, while cores produced from a relatively highly doped material showed a small decrease in conductivity. The results suggest that the manufacturing process has introduced significant amount of impurities to the silicon core, which corresponds to additional charge carriers.