Experimental results of a single-photon avalanche diode (SPAD) based optical fiber receiver integrated in 0.35 µm PIN-photodiode CMOS technology are presented. To cope with the parasitic effects of SPADs an array of four receivers is implemented. The SPADs consist of a multiplication zone and a separate thick absorption zone to achieve a high photon detection probability (PDP). In addition cascoded quenchers allow to use a quenching voltage of twice the usual supply voltage, i.e. 6.6 V instead of 3.3 V, in order to increase the PDP further. Measurements result in sensitivities of -55.7 dBm at a data rate of 50 Mbit/s and -51.6 dBm at 100 Mbit/s for a wavelength of 635 nm and a bit-error ratio of 2 × 10-3, which is sufficient to perform error correction. These sensitivities are better than those of linear-mode APD receivers integrated in the same CMOS technology. These results are a major advance towards direct detection optical receivers working close to the quantum limit.