We have fabricated a 2-mm gap semi-insulating GaAs photoconductive semiconductor switch (PCSS), and obtained a 1.45-kA large current under a bias voltage of 6 kV when the PCSS was triggered by a 4- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">\(\mu \) </tex-math></inline-formula> J commercial laser diode. An RLC transient circuit model was employed to get the electrical properties of the PCSS in the transient discharge process. The reason for the switch exiting from nonlinear operating mode was that the electric field across the switch dropped below the lock-on field. This letter shows the attractive prospect of a low-cost compact high-power pulse source with the GaAs PCSS.