Stable triggering of acquisition devices is critical to accurately measure electromagnetic transients, especially for very fast transient overvoltages (VFTOs). A highly stable and lowcos t self-trigger method for transient measurement is proposed. An integrated low-voltage arm module was developed to synchronously realise the triggering and VFTO measurement. The trigger branch was developed using a high-pass filter. This component obtained the high-frequency component of the VFTO to trigger the oscilloscope. The trigger branch was integrated with the measurement branch through an impedance converter. An attenuator was implemented before the impedance converter to avoid overvoltage damage to the chip. The circuit parameters of the attenuator were optimised to alleviate the disturbance of the measurement branch. The calibration results demonstrated that the �1 dB bandwidth of the measurement branch in this system ranged from 11.8 Hz to 105 MHz. The low cutoff frequency of the trigger branch was 710 Hz. The VFTO waveforms generated by the operation of a disconnector in a real 252 kV gas insulated switchgear were measured using the proposed system. The test results verified that the self-trigger measurement system can provide stable trigger signals and accurately measure the VFTO waveforms.