Silicon drift detectors (SDD) have shown an excellent energy resolution close to room temperature. All signal charges, generated in the fully depleted volume by ionizing radiation are guided to a small electron collecting read-out node. The first amplification is realized with an integrated on-chip JFET. The total read-out capacitance can be kept below 250 fF, independent of the detector area. The fact, that the first amplifier is already integrated in the detector offers many operational advantages: (a) better resolution because of the reduction of read-node capacitance, (b) insensitivity with respect to acoustic noise and electrical pick-up, (c) compact detector packaging and (d) the absence of liquid nitrogen cooling. Fig. 1 shows the detector concept, including the integrated electronics. The X-rays are hitting the SDD from the homogeneous radiation entrance window on the backside of the device.