Mathematical simulation and experimental studies of an MINpn(MISSS) metalconducting insulator-semiconductor bipolar transistor are described in the paper. Such devices generally have switching characteristics. The high-impedance state is associated with a reversebiasedp-njunction which sustains high voltages. The breakover occurs when the sum of the small-signal current gains reaches unity. The low-impedance state is associated with an accumulation of the semiconductor surface which increases the electric field across the insulator. The energy bandshift may cause the valence-band edge of the semiconductor to be at a higher energy level than the metal-work function. The metal-insulator-semiconductor (MIS) acts as a minority diode and has a large flow of valence electrons. The second regenerative feedback may create the intermediate stable state, if the positive resistance appears prior to the second breakover. The simulation results show that this intermediate stable state may happen when the oxide thickness is within a certain (tunnelling) range. The larger barrier height device (majority diode) has a greater possibility of exhibiting the intermediate stable state. The narrower basewidth device is more significant in indicating the voltage collapse. The experimental result confirmed the existence of the intermediate stable state.