The electrical behaviour of lateral bipolar transistors has a large effect on latch-up phenomena; in particular in the region between low level and high level injection, where the parasitic thyristor is switching on. By solving the continuity equation in this region under some approximations the base and collector current can be calculated rather accurately if the lifetime of the minority carriers in the base is known. The influence of this parameter is very important; therefore a few measurement techniques are discussed and the influence of the lifetime on the electrical characteristics is shown. Finally a comparison between the holding current, implementing and neglecting the odd shape of the beta in the transition region between high and low level injection, is made.