We investigate the relative transmission and the effective gain of a two-dimensional electron gas (2DEG) in the terahertz (THz) frequency domain. The position of THz source, device, and detector is numerically simulated in order to obtain an optimized experimental configuration. The effect of variation of polarization of incident beam, and geometries of devices is investigated. The inter-digitated finger (IDF) structures of the device under investigation show maximum transmission in direct polarization configuration which is attributed to the metallic polarizing nature of IDFs, and to the effective interaction of the incident THz radiations and the device. This technique should be helpful to measure THz transmission of electronic devices with 2DEG.