Organic semiconductors are candidates for use in next-generation thin film electronics. In many of these applications, electrical doping can increase effective carrier mobilities by filling trap states, enhance electrical conductivity by increasing the density of free charge carriers, and/or can lower barriers to charge-carrier injection or collection at electrodes. An emerging application is the use of semiconducting polymers as thermoelectric materials. The performance of thermoelectrics is related to their electrical conductivity, thermopower and thermal conductivity which are all functions of the carrier concentration. We will discuss our efforts to understand how the electrical conductivity and thermopower of semiconducting polymers are interrelated using model polymer systems including poly(3-hexylthiophene) and a thienothiophene-based polymer, PBTTT. We find that changes in processing conditions can increase the electrical conductivity by >50x at the same apparent carrier concentration, while causing smaller changes in the thermopower for PBTTT. The increase in performance can be understood by the nanoscale connectivity between ordered domains and quantitated using synchrotron-based X-ray scattering methods and temperature-dependent thermopower and transport measurements. The role of the miscibility of dopants and polymers will also be discussed as a critical factor in controlling their electrical conductivity.