Electrochemical doping and in-situ UV-vis-NIR spectroelectrochemical properties of solid films of some sigma-pi conjugated polymers consisting of alternating oligothienylene units and silylene units have been investigated in acetonitrile, while chemical doping of these polymers has been conducted in dichloroethane. The cyclic voltammograms of the films of these polymers show two couples of redox peaks in the potential range of 0-1.2 V. The doping-level measurements and the in-situ spectroelectrochemical measurements suggest that the repeat unit of the polymer chain is oxidized to the radical cation in the first-step oxidation, and to the dication in the second-step oxidation. In addition, the in-situ UV-vis-NIR measurements provide clear-cut evidence for the transitions from the radical cation to their pi-dimers via a coupling reaction. The changes in the absorption spectra of the polymer films at different potentials are interpreted by considering the dimerization reaction of the radical cations to the pi-dimers.