Transient phenomena which accompany the breakdown of gas in a semiconductor-gas discharge (SGD) system with 100 &mgr;m interelectrode distance have been studied experimentally and with numerical calculations. This system serves as the basis for an image converter operating in the infrared (IR) spectral region. The experiments are done for a cryogenic discharge in helium at a temperature close to that of liquid nitrogen. Depending on specific experimental conditions, oscillatory or aperiodic modes approaching to the steady-state current are observed after breakdown has been induced by a step-like voltage pulse. Numerical calculations of transient phenomena were performed for experimental conditions within the framework of the Townsend model, taking into account direct ionization, Penning ionization and secondary emission of electrons from the cathode. The main features of discharge kinetics obtained are in accordance with experimental data. At the same time, with the steady-state discharge current density varying fromj= 1×10−4A/cm2to7×10−2A/cm2,inconsistencies between experimental and theoretical results are observed. A possible reason for this discrepancy is related to the complex process of secondary ionization at the cathode under the conditions of a cryogenic discharge and to the dependence of the secondary electron emission factor on current density, that has been neglected in constructing the model. The results obtained are considered from the viewpoint of the response time of gas-discharge IR image converters. ©1997 American Institute of Physics.