Reliability testing of power semiconductor devices is required by customers and reliability standards like the JESD22 and AEC-Q100. Conventional test systems feature the application of fixed stress patterns for a large amount of devices in an environmental chamber at the same time. However, reading status information or acquisition of analog measurements is usually not performed due to the missing return signal interface. Previous efforts have already succeeded at providing these necessary measurement capabilities, although at the cost of complexity of the test setup. The reliability test system architecture in this thesis presents a new, modular test system approach. Due the availability of microcontrollers for the automotive temperature range (up to 125 ÂC), a small networked controller module can be placed close to the tested device inside the environmental chamber. Therefore, the stimuli and measurement signal lines are local and the signal quality is improved. In order to provide the required flexibility, the microcontrollers use a serial bus interface to communicate with a host computer. The host distributes the test programs to the control modules and synchronizes their actions. Furthermore, the host is used for controlling externally connected instruments as well as visualizing and storing measurement data. The test procedure for individual devices can be created without the need to change and re-compile the microcontroller firmware. The test control is based on the finite state machine model. The model can be changed when the controller is in idle state. Furthermore, the Lua script interpreter is proposed to control and measure the tested devices through the microcontroller periphery. To create the test programs for this modular test system, the Testplan-Builder tool is provided. It has knowledge about the configuration of the used hardware targets and the Lua functions to help the users design their test application. The test plan is transferred to the microcontrollers via the communication channel. Three different test application examples demonstrate the versatility and performance of the new modular test system.