The present invention relates to a device for thermal cycling of biological samples, a heat sink used in such a device and a method. The heat sink comprises a base plate designed to fit in a good thermal contact against a generally planar thermoelectric element included in the device, and a plurality of heat transfer elements projecting away from the base plate. According to the invention, the heat transfer elements of the heat sink and arranged in a non-parallel configuration with respect to each other for keeping the temperature of the base plate of the heat sink spatially uniform during thermal cycling.