Abstract: Detector for terahertz radiation with a micro-plasma cell (1) having a cavity (5) including a plasma in operation when applying a DC bias to the micro-plasma cell (1). Furthermore, the detector is provided with read-out electronics (20) connected to the micro-plasma cell (1). The read-out electronics measure changes of an electron density in the plasma in the micro-plasma cell (1) with respect to the DC bias provided electron density. The cavity (5) includes a gas composition near atmospheric pressure or higher, and the gas composition includes a Penning mixture.