A device for the thermal treatment of test samples is presented. The device comprises a sample holder and one or more thermoelectric elements which are in thermal contact with the sample holder. The sample holder comprises at least two holding positions configured to hold test sample consumables. The sample holder comprises an internal working fluid and a hollow body with an inner bottom surface and an inner top surface connected to each other with a pillar. The pillar extends along a vertical axis perpendicular to the inner bottom surface and substantially in the middle of the distance between the at least two holding positions. A laboratory instrument and a method for the thermal treatment of test samples is also presented.