A high voltage, high di/dt, modular solid state switch intended to replace thyratrons in high power modular applications is under development. This paper describes the results of testing a switch module with a 10kV, 6kA, 30 kA/microsecond, 3ms PFN, under normal and load fault conditions. Included are data on switching losses and thermal performance during repetition rate operation. Experiments using alternate PFN's to obtain higher di/dt operation are discussed. Initial results of multiple module tests with a 30 kV PFN are presented. The switch module uses three 5kV, 15mm diameter, thyristors connected in series. These thyristors were developed specifically for pulsed power applications, and have an interdigitated gate/cathode geometry to minimize turn-on losses and maximize di/dt. The module's trigger circuit uses the switched energy to drive the thyristor gates, eliminating the need for an external gate drive power supply. A 35V, 1A, 50ns risetime pulse triggers the module. The total switch inductance is <50nH, if the case is used as the return current path. The compact, economical, modular package design facilitates the development of drop-in replacement switches for thyratrons with voltage ratings of >60kV. Work supported by U.S. Department of Energy, grant DE-FG02-00ER82948.Presenting Author : Glidden C.