An electrochemical sensor, used with a measuring medium, has a sensor head (1), a sensor chip (6, 606) with a sensitive region (632), a sensor body (2) with an end piece (3, 503), a sealing means (10, 510, 610) and a pressing element (18, 618). The sensor body is connected to the sensor head. The end piece is hollow with a closed end region and a measuring opening (4, 504) that allows the measuring medium to contact the sensitive region, which is inside the end piece during operation. The sealing means surrounds the measuring opening, other than the sensitive region, and seals the inside of the end piece from the measuring medium during operation. The pressing element biases the sensor chip against the sealing means and the edge of the measuring opening. The end piece has an integral, gap-free design in the region that contacts the measuring medium during operation.