The klystron modulator for the Japan Liner Collider (JLC) requires to produce a 500 kV, 530 A, 1.5 microseconds flat-top pulse to drive a pair of 75 MW PPM-klystrons. KEK has programs to improve reliability, energy efficiency and costs of modulators. Two main studies are under way. The first is to improve the line-type modulator by use of solid-state switch that can be used instead of thyratoron. We have developed a solid-state switch which consists of 15 SI-thyristors stacked in series. The switch has been successfully operated at 45kV hold-off voltage, 6000A peak current, 6 microsecond pulse-width and 25Hz. The second is to develop a direct switching modulator with a solid-state switch and a pulse transformer. This modulator uses a 1:5 primary split pulse transformer and multiple solid-state IGBT modules stacked in series. To study this type of modulator, a ten-stacked model modulator has been assembled and successfully tested. In this paper, we will describe the modulator design, and the experimental results of both the solid-state switch and the model modulator.Presenting Author : Akemoto M.