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Summary form only given, as follows. A repetitive pulsed power modulator, which uses high voltage static induction thyristors as main switching devices, has been designed and constructed for the application to a discharge light source. The main components of modulator are a pulse forming network (PFN) with 20 stages, a magnetic switch with a reset circuit and a stacked semiconductor switch. The PFN consists of 100 ceramic capacitors (each capacitance is 2000pF, 30kV) connected in parallel. The resulted electrical length, capacitance and impedance of the PFN are 213 ns, 0.283 uF and 0.75 ohm, respectively. A current source, which provides 8 A, is used for resetting the magnetic switch. The leakage current flowing when the magnetic switch is unsaturated can be used as a pre-ionization current. The semiconductor switch is made of 3 high voltage static induction thyristors connected in series. In order to get a high di/dt, it is important to supply a high gate current with a short risetime. Therefore, an inductive storage type gate driver, which is driven by an external optical signal, was made to provide a very large di/dt current to the gate. The significant feature of the static induction thyristor is that it has very low ON-state voltage. This feature is especially suitable for high rep-rate operation of pulsed power modulators, since energy loss by the switch can be remarkably reduced. When the PFN was charged to 9 kV, the load voltage of 4 kV and the load current of 5 kA were obtained for the load resistance of 0.7 ohm. The measured risetime of current is 203 ns and the efficiency of 91% is obtained.