[en] The Medipix2 chip is a pixel detector readout chip consisting of 256x256 identical elements, each working in single photon counting mode for positive or negative input charge signals. The chip is designed and manufactured in a six-metal 0.25 μm CMOS technology. This paper describes several electrical measurements which have been carried out on the chip prior to detector bump bonding using a dedicated readout system. Threshold linearity and variation has been measured for both electron and hole collection. The noise is ∼100e^- RMS and the threshold can be adjusted to ∼120e^- RMS for both polarities. The minimum operating threshold is ∼1000e^-