Understanding of thermally activated charge transport in polymer semiconductor thin-films is absolutely required because of its critical role in performances of the devices for flexible and stretchable electronics.Here,we describe the first 3-dimensional charge conduction and molecular scale investigation about its origin in polymer semiconductors via comparative analysis using the isoindigo-based polymers with a siloxane-terminated side-chain(PII2T-Si)and a branched alkyl-terminated side-chain(PII2T-Ref).Interestingly,for PII2T-Si thin-film with a bimodal molecular orientation,unlike PII2T-Ref with a unimodal fashion,the distinct transition of the relevant crystallographic parameters including the π-stacking distance and the coherence length of the lateral crystallites was observed at different temperature regimes,thereby strongly mediating 3-dimensional charge conduction into the channel.We believe that our findings will provide rational design rule to guide next generation polymer semiconductors for high-performance flexible organic electronics.