Solid-state properties of undoped gels of poly(3-n-octylthiophene) (POT) are investigated by N-2 BET surface measurements, X-ray diffraction and small-angle X-ray scattering (SAXS) experiments. The observed variations in compacity, crystalline domain sizes and typical sizes of large-scale heterogeneities versus the crosslink ratio, R-i, all exhibit an extremum for the gel R-i = 1/100. As reported earlier. this gel in the doped state also exhibits the highest conductivity. A major interest in the crosslinking process is to enhance the conductivity by modifying POT crystallinity, A deeper understanding of the crystallization mechanisms should therefore allow one to master the transport properties in POT systems.