A cascode switch device includes a cascode circuit, which includes a first switch and a second switch, and a protection circuit. The protection circuit is coupled between the first switch and the second switch. A first leakage current passing through the protection circuit is greater than or equal to a difference between a second leakage current and a third leakage current, and is smaller than an upper limit value of a leakage current of the cascode circuit. An upper limit value of a withstanding voltage is present between the first terminal and the control terminal of the first switch. When the first switch operates at the upper limit value of the withstanding voltage, the second leakage current is an upper limit value of a leakage current passing through the first switch, and the third leakage current is a lower limit value of a leakage current passing through the second switch.