A new kind of ultra-fast power photoconductive semiconductor switch with double-layer semi-insulating GaAs:EL2 is designed and prepared. Because the distribution of voltage between the triggered double GaAs layers is dynamic, when biased at a high electric field, the double layers go into the high-gain state one after the other but prevent each other from entering the Lock-on state, so the output electric pulse has double peaks and looks like a rectangular wave. This working mode not only has the strong points of the nonlinear mode, such as the required laser energy is far less and the rise time is shorter than that of the linear mode, but also has the merits of the linear mode, such as the repetition frequency is higher and the life is far longer than that of the nonlinear mode. Biased at 6500 V and triggered by an 8 ns, 3 mJ and 1064 nm laser pulse, the rise time of the output electric pulse is 13.2 ns, the fall time is 54.6 ns, the full width at half maximum is 148.4 ns, the first peak is 885 V and the second peak is 897 V. With the bias voltage increasing, the rise time nearly keeps a constant, the width and fall time decrease slightly and the double peaks increase obviously.