The self-assembly of colloidal building blocks into complex and hierarchical structures offers a versatile and powerful toolbox for the creation of new photonic and optoelectronic materials. However, well-defined and monodisperse colloids of semiconducting polymers, which would form excellent building blocks for such self-assembled materials, are not readily available. Here we report the first demonstration of a Suzuki-Miyaura dispersion polymerization; this method produces highly monodisperse submicrometer particles of a variety of semiconducting polymers. Moreover, we show that these monodisperse particles readily self-assemble into photonic crystals that exhibit a pronounced photonic stopgap.