The partial oxidation of an ordered macroporous silicon membrane (see figure and cover) with different pore-wall thicknesses results in a regular compartmentalized structure Of SiO2 domains separated by opaque silicon walls. Experimental conditions ensure the flatness of the partially oxidized macroporous silicon. Fluorescence crossover is minimized within the photonic crystal, enabling its use as microarray support for sensitive bioanalytics, demonstrated with a DNA-hybridization experiment.