Semiconductor device and power conversion device

Abstract

Provided is a cascode-type semiconductor device configured by connecting a plurality of power transistors in series. The semiconductor device is highly reliable and has a high design / fabrication degree of freedom in that a normally-off power transistor can be used for each of the power transistors, the source-to-drain withstand voltage and the gate-to-source withstand voltage of each of the power transistors can be designed independently, and the withstand voltage of the semiconductor device as a whole does not significantly decrease even in the case where there is a failure in the source-to-drain withstand voltages of some power transistors. The present invention is a semiconductor device provided with a plurality of multistage-connected semiconductor elements in which a drive signal from a gate drive circuit is input to the gate in the first stage and in which the drain in a preceding stage is connected in series with the source in the following stage. The semiconductor device is characterized in that: the plurality of semiconductor elements are first-conductivity-type MOSFETs if one of the N type and the P type is defined as a first-conductivity type and the other as a second-conductivity type; one or more first second-conductivity-type MOSFETs that, when an on drive signal is input from the gate drive circuit to the gate of the semiconductor element in the first stage, turn on the semiconductor elements in the second and following stages by supplying the on drive signal to the semiconductor elements in the second and following stages are provided; and one or more second second-conductivity-type MOSFETs that, when an off drive signal is input from the gate drive circuit to the gate of the semiconductor element in the first stage, turn off the first second-conductivity-type MOSFETs and turn off the semiconductor elements in the second and following stages by supplying the gates of the semiconductor elements in the second and following stages with the voltage at the source or drain of the semiconductor element in the preceding stage are provided.

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