Optical transient switching measurements of the metal-insulator (tunnel)-silicon thyristor (MIST) are presented. A pulsed GaAlAs laser operating at 0.85 μm wavelength was employed to obtain the turn-on delay time and the rise and fall times of the MIST as a function of optical power level, bias and pulse width. The turn-off delay time was also measured under the same conditions, and the results are explained qualitatively. Furthermore, the response of the device under minimum threshold conditions is established, and the facility of the measured data in predicting the performance of the MIST as a monostable optical detector is examined. Finally, areas for further improvement are outlined.