The invention relates to an X-ray detector for detecting X-radiation, as used, in particular, in computer tomographic (CT) systems. The X-ray detector in accordance with the invention is composed of a photo sensor device, which comprises individual detector elements (1), above which scintillator elements (2) are disposed. These convert the incident X-ray light (6) into visible or UV light (7), which is detected by a photodiode (4) located on the detector element (1). In accordance with the invention, a micro-lens (3), which focuses the light (7) departing from the scintillator element (2) onto the photodiode (4), is disposed between the scintillator element (2) and the detector element (1). It is possible, in this manner, to use large areas of the detector element (1) for further electronic components (5) outside the photodiode (4), and, at the same time, to ensure a high DQE (Detection Quantum Efficiency) in that the light (7) departing from the scintillator element (2) is virtually fully exploited. The crosstalk from scatter radiation from adjacent detector elements is effectively prevented simultaneously.