Abstract:  The fundamental structures and working principles of the new-type power device MCT （MOS-con-trolled Thyristor） were introduced‚and the physical state model in turn-off status modeled mathematically by the state-average method was discussed．The whole device was regarded as a system‚whose stability was analyzed by the state-space analytical method．Thereby the maximum controllable turn-off current of MCT‚and the relationship between the current and MCT’s structural parameters were deduced．The validity of conclusions drawn here was proved using MATLAB／Simulink．

Key words: field effect, thyristor, state-space analytical method, maximum controllable turn-off current, state model, structural parameter