Back-illuminated silicon photomultipliers having a substrate of a first conductivity type having front and back sides, a matrix of regions of a second conductivity type in the substrate, a matrix of regions of the first conductivity type under the matrix of regions of the second conductivity type and adjacent the back side of the substrate, with the bottom of the matrix of regions of the second conductivity type forming a p/n junction with the substrate or a matrix of regions of the second conductivity type, the matrix of regions of the first conductivity type having a higher conductivity than the substrate, a common anode formed by a uniform layer of the first conductivity type of higher conductivity than the substrate on the back side of the substrate. Preferably a plurality of trenches filed with an opaque material are provided in the back side of the substrate, the substrate preferably having a thickness of less than approximately 150 um.