Abstract: A four-gap, rail gas switch for fast linear transformer drivers (LTDs) has been developed to be of low jitter and low inductance, by using four horizontal gaps constructed by rail electrodes. The electric field of the switch and the hold-off voltage of the single gap of 8 mm were calculated by using electric field numerical simulation and Meeks Criterion analysis, respectively. A probability analysis method, for predicting self-breakdown voltages of a switch consisting of several gaps in series, is put forward. The calculated self-breakdown voltages were in agreement with the experimental results. The switch inductance of no more than 109 nH provides the LTD brick a measured inductance of 290 nH. The relative standard deviation of self-breakdown voltage is about 1.5%. Under a 60 kV forward voltage pulse, the switch with 48%-74% voltage ratio has a close jitter of 0.9-2.6 ns. Compared with a previously developed switch with toroidal electrodes, the rail gas switch has a lower trigger voltage and self-breakdown stability while operating at the same voltage ratio.