The charge sharing effect in pixel semiconductor detector is a theoretically well described phenomenon where the charge created by the particle spreads out during the charge collection process and it can be finally collected by several adjacent pixels forming a cluster. However, the experimental confirmation of models describing charge sharing has been little investigated and difficult to realize. The novel semiconductor pixel detector Timepix (newly developed successor of the Medipix2 device developed by Medipix collaboration) stands as a perfect tool to explore this effect. The device consists of a semiconductor detector chip (300 μm thick silicon) bump-bonded to a readout chip. The detector chip is equipped with a single common backside electrode and a front side matrix of electrodes (256 x 256 square pixels with pitch 55 μm). These pixels behave like independent channels each with devoted read-out electronics. In the so-called Time-Over-Threshold mode, Timepix enables direct energy measurement in each pixel. This contribution shows the experimental results of probing charge collecting processes acquired with radiation sources and the Timepix detector. The cluster size dependencies on changing conditions such as bias voltage and temperature were measured and evaluated.