In this paper, we present the conception, fabrication and characterization of a room temperature thermopile designed to detect electromagnetic fields at 3 THz. The absorber consists of a metallic grid made of one of the material of the thin film thermocouples. The design of the grid is based on a theoretical multilayer model using equivalent resistivity and taking into account small diffraction effects. For future work with sub-wavelength resolution, we have also studied the effect of the reduction of the size of the grids on the equivalent resistivity. The grid is deposited on a 1.5 mm-radius SiO2 circular membrane. The time constant of the sensor is measured with THz and optical sources and it is consistent with finite elements simulations. The sensitivity and the limit of detection are also evaluated. First results at 0.3 THz (and not at the designed frequency of 3 THz, because of limitations in the testing equipment) show a sensitivity of 35 nV/(W/m2) and a limit detection of the E-field of 23 V/m due to a significant amount of noise. Future perspectives are put forward to increase the sensitivity.