Thin-film lateral n-p-n bipolar transistors (BJT) have been fabricated in moving melt zone recrystallized silicon on a 0.5-µm silicon dioxide substrate thermally grown on bulk silicon. Current-voltage characteristics of devices with different base widths (5 and 10 µm) have been analyzed. The use of a metal gate over oxide covering the base region has allowed the devices to be operated as n-channel MOSFET's as well thus surface effects on device characteristics have been investigated under varying gate-bias voltages. Maximum dc current gain values of 2.5 were achieved with a 5-µm base width and values around 0.5 with a 10-µm base width. Higher gain values were impeded by onset of high-level injection which occurred at low currents because of light base doping of these devices.