A 48-element monolithic matrix detector, designed for easy and efficient coupling to input optical systems, has been fabricated and tested. The pixels are single photon avalanche diodes (SPAD) with 50 μm diameter, ordered in a 8x6 array with 240 μm pitch. The photon detection efficiency is remarkably uniform over the array, with 48% peak value at 530 nm and better than 30% value over all the visible range. Low dark counting rate (DCR) is obtained in operation at moderately low temperature (-15 C with Peltier element cooling): the individual pixel DCR is 60 cps for about 40% of the elements and is below 5700 cps in the rest of the array. It was verified that the afterpulsing probability is below 1% and that the optical crosstalk probability between elements is lower than 0.002.