jats:titleAbstract</jats:title>jats:pThe measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (jats:italicT</jats:italic>jats:subg</jats:sub>) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the jats:italicT</jats:italic>jats:subg</jats:sub> of a range of state‐of‐the‐art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field‐effect transistors. We compare our measured values for jats:italicT</jats:italic>jats:subg</jats:sub> to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the jats:italicT</jats:italic>jats:subg</jats:sub> values agree well with theoretically predictions. However, for the near‐amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for jats:italicT</jats:italic>jats:subg</jats:sub> appear to be significantly higher, predicted by theory. However, values for jats:italicT</jats:italic>jats:subg</jats:sub> are correlated with the sub‐bandgap optical absorption suggesting the possible role of the interchain short contacts within materials’ amorphous domains.</jats:p>