A design of high voltage switch module based on a stack of Metal Oxide Semiconductor Field-Effect Transistor(MOSFET) is put forward. By stacking 20 RF MOSFETs with Uds of 1 kV, the switch module shows high speed and high repeat frequency, and can operate above 10 kV. The structure of high voltage switch module, a unit circuit using one RF MOSFET switch and a method of cooling the switch are designed. A pulse generator circuit based on the high voltage switch module is simulated. A 10 kV pulse generator is created by the stack. The turn-on time of pulse generated by experimental device is lower than simulated result.