Traditionally, Single Photon Avalanche Diodes (SPADs) are fabricated using dedicated processes that require additional technological steps when compared to standard CMOS. Instead, this paper presents the design of SPADs that attain good performances, by using a standard high-voltage CMOS process. The detector is monolithically integrated together with an Active Quenching Circuit (iAQC), a counter, and a serial communication interface. This opens the way to the design and fabrication of ultra compact multi-channel single-photon counters.