In my thesis, I investigated a thermal test structure of a terahertz (THz) frequency electromagnetic wave sensitive microsensor with working principle based on the thermal-electric Seebeck effect. The device was made in the Institute for Technical Physics and Materials Science, Hungarian Academy of Sciences. The thesis contains steady-state and transient thermal-electric finite element simulations. To provide the three dimensional modelling of the geometry, I wrote a C program, which generates executable code for the modelling software from the layouts of the photolithography. I carried out approximation analytical calculations to solve the two dimensional heat conduction equation that show good agreement with the simulations in case of vacuum. At the end of the study I characterized the steady-state and time dependent response of the sensor. For the automated instrument control and data acquisition, I made programs with graphical user interface in LabVIEW environment.