To guarantee sufficient surge current fault protection for power electronic converters, power semiconductors have to be tested under appropriate surge current conditions. Standard maximum surge current values include the permissible fault current amplitude, or the I2t-value; however, they might not be sufficient to describe a power semiconductor's performance under all potential fault conditions. Surge current sources based on passive components are state of the art, but are limited to usually only one specific current waveform. This paper describes the topology and the design of a new modular and highly dynamic Surge Current Source for power semiconductor tests with adjustable current waveforms. The new modular converter concept is introduced, with two potential operation modes: High Current Mode (HCM) and Dynamic Current Mode (DCM). The requirements for the Surge Current Tester are defined, and the electrical and mechanical design are described, including the modulation scheme and control. Experimental investigations prove the function of the current source with peak currents up to 100 kA (HCM) and the realization of highly dynamic load current trajectories with peak currents up to 50 kA (DCM). The output current ripple is exceptionally small with a theoretical value of below 1 %.