Heteroepitaxial films of silicon-on-sapphire were used to fabricate lateral bipolar n-p-n transistors. The devices have a common-base direct-current amplification factor of 0.9 and a maximum frequency of oscillation of 2.4 GHz. As a result of the vertical p-n-junction arrangement, small junction areas are possible, e.g. 1×10−6cm2, which yield depletion-layer capacitances of 0.02–0.05 pF.