A radiation detector comprises an electrode structure (19,4,35), a planarising layer (101) being disposed over the electrode structure and a protective stack (103,104,105) which covers the planarising layer. The planarising layer evens out substantial differences between levels of the electrode structure above the substrate on which the electrode structure is disposed. Consequently, cracks, weak spots and other defects in the protective stack are to a large extent avoided. Because the planarising layer covers essentially the entire electrode structure, practically all sources of defects, notably cracks, in the protective stack are avoided.