A new synthetic route to hyperbranched polymers is developed. Polycyclotrimerizations of functional diynes 1-3 initiated by a simple base of piperidine lead to the formation of hyperbranched poly(aroylarylene)s P1-P3 with perfect 1,3,5-regioregularity and high degree of branching (up to 100%) in high yields (up to 99%). The polymers show high photosensitivities and can be readily photo-crosslinked to give photoresist patterns with nanometer resolutions.