An apparatus for determining the temperature of microfluidic devices, or portions thereof, with at least one flat region suitable for heat transfer, wherein said apparatus comprises: - housing means adapted for receiving and holding the microfluidic device in a certain position and orientation such that in this position, the flat region of the microfluidic device establishes a certain reference plane, - a movable module that is movable at least according to a direction X-X' perpendicular to the reference plane, where the movement establishes at least one approaching position with respect to the microfluidic device and a separated position with respect to the microfluidic device, where this movable module comprises: ∘ a pressure element (2.1) that is movable according to direction X-X', where the movement is guided with respect to the movable module, and where said pressure element (2.1) has clearance to allow being misaligned with respect to direction X-X', ∘ a heat source (2.3) located in the pressure element (2.1), where in the approaching position, the heat source (2.3) comprises a contact surface (2.3.1) adapted for being supported on the heat transfer region of the microfluidic device and transferring heat through said region, ∘ a compressible pressure spring (2.2) located between the movable module and the pressure element (2.1) such that when the movable module is located in the approaching position with respect to the microfluidic device, said spring (2.2) is compressed, exerting force against the pressure element (2.1) and said spring (2.2) in turn applying pressure on the heat transfer region of the microfluidic device by means of the contact surface (2.3.1). - housing means adapted for receiving and holding the microfluidic device in a certain position and orientation such that in this position, the flat region of the microfluidic device establishes a certain reference plane, - a movable module that is movable at least according to a direction X-X' perpendicular to the reference plane, where the movement establishes at least one approaching position with respect to the microfluidic device and a separated position with respect to the microfluidic device, where this movable module comprises: ∘ a pressure element (2.1) that is movable according to direction X-X', where the movement is guided with respect to the movable module, and where said pressure element (2.1) has clearance to allow being misaligned with respect to direction X-X', ∘ a heat source (2.3) located in the pressure element (2.1), where in the approaching position, the heat source (2.3) comprises a contact surface (2.3.1) adapted for being supported on the heat transfer region of the microfluidic device and transferring heat through said region, ∘ a compressible pressure spring (2.2) located between the movable module and the pressure element (2.1) such that when the movable module is located in the approaching position with respect to the microfluidic device, said spring (2.2) is compressed, exerting force against the pressure element (2.1) and said spring (2.2) in turn applying pressure on the heat transfer region of the microfluidic device by means of the contact surface (2.3.1). ∘ a pressure element (2.1) that is movable according to direction X-X', where the movement is guided with respect to the movable module, and where said pressure element (2.1) has clearance to allow being misaligned with respect to direction X-X', ∘ a heat source (2.3) located in the pressure element (2.1), where in the approaching position, the heat source (2.3) comprises a contact surface (2.3.1) adapted for being supported on the heat transfer region of the microfluidic device and transferring heat through said region, ∘ a compressible pressure spring (2.2) located between the movable module and the pressure element (2.1) such that when the movable module is located in the approaching position with respect to the microfluidic device, said spring (2.2) is compressed, exerting force against the pressure element (2.1) and said spring (2.2) in turn applying pressure on the heat transfer region of the microfluidic device by means of the contact surface (2.3.1).