The dark count rate is measured by integrating the pedestal spectrum above a given threshold. The threshold (in photoelectrons) is computed using the gain and pedestal values as determined from the light pulser spectra. The noise rates shown in figures 8 and 7 are the count rates for a threshold of 0.5 photoelectrons. Typical values at standard operating conditions are around 200 kHz, a factor of 20-30 higher than achieved with both earlier SSPM and later VLPC generations; the excessive noise, which nevertheless does not compromise the use of these devices in our tracking application [8], is attributed to an antimony contamination in the boundary between blocking (intrinsic) and gain layer.