Abstract: A thermopile sensor for detecting infrared radiation arriving in an axial entering direction. The thermopile sensor comprises a metal housing that has a base section and a mantle section, a cavity between said mantle section and said base section, an opening in said mantle section opposite said base section for entering of said infrared radiation, thermopile chip on a top surface of the base section, electrical connectors connected to said thermopile chip(s) and which extending through said metal, and a radiation transparent window. Said thermopile sensor is a miniature sensor construction, in which said cavity has an inner dimension adapted for at least one thermopile chip. Said base section has an outer base dimension and a base thickness forming the first part of a thermal mass, and said mantle section extends with a length from said base section and has a wall thickness around said opening forming a second part of said thermal mass, which surrounds said thermopile chip.