The surface electrical conductivity of sapphire in the presence of caesium vapour has been measured for a variety of Cs pressures,PCs, and sample temperaturesTs. Data is presented for Cs pressures in the range 10−4to 1 Torr and sample temperatures ranging from 600 to 820 K. The conductivity dependence onPCsat constant values ofTsis weak over the measured range. The small variations observed have a non‐monotonic dependence onPCs. Experiments whereTsis varied at constantPCsshow that below a critical temperature the conductivity decreases with increasing values ofTs. However above this critical temperature the trend is reversed. © 1995American Institute of Physics