The invention concerns a thermopile sensor for detecting infrared radiation (R) arriving in an axial entering direction (E). The thermopile sensor (30) comprises a metal housing (10) that has a base section (11) and a mantle section (12), a cavity (39) between said mantle section and said base section, an opening (41) in said mantle section opposite said base section for entering of said infrared radiation, thermopile chip (33) on a top surface (13) of the base section, electrical connectors (36) connected to said thermopile chip(s) and which extending through said metal, and a radiation transparent window (43). Said thermopile sensor (30) is a miniature sensor construction, in which said cavity has an inner dimension adapted for at least one thermopile chip (33). Said base section has an outer base dimension (D2) and a base thickness (H) forming the first part (31) of a thermal mass (M), and said mantle section extends with a length (L) from said base section and has a wall thickness (S) around said opening forming a second part (32) of said thermal mass (M), which surrounds said thermopile chip. Electrical connectors are metal film leads (14) on an electrical insulation membrane (15).