Cross-talk characterization results of high-fill-factor single-photon avalanche diode (SPAD) arrays in CMOS 150-nm technology are reported and discussed. Three different SPAD structures were designed with two different sizes (15.6 and pitch) and three guard ring widths (0.6, 1.1, and ). Each SPAD was implemented in an array, composed of 25 () devices, which can be separately activated. Measurement results show that the average cross-talk probability is well below 1% for the shallow-junction SPAD structure with pitch and 39.9% fill factor, and 1.45% for the structure with pitch and 60.6% fill factor. An increase of cross-talk probability with the excess bias voltage is observed.