Abstract Here we present a method to control the size of the openings in hexagonally organized BCP thin films of poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) by using surface reconstruction. The surface reconstruction is based on selective swelling of the P4VP block in ethanol, and its extraction to the surface of the film, resulting in pores upon drying. We found that the BCP pore diameter increases with ethanol immersion temperature. In our case, the temperature range 18 to 60 °C allowed fine-tuning of the pore size between 14 and 22 nm. A conclusion is that even though the molecular weight of the respective polymer blocks is fixed, the PS-b-P4VP pore diameter can be tuned by controlling temperature during surface reconstruction. These results can be used for BCP-based nanofabrication in general, and for vertical nanowire growth in particular, where high pattern density and diameter control are of importance. Finally, we demonstrate successful growth of indium arsenide InAs vertical nanowires by selective-area metal-organic vapor phase epitaxy (MOVPE), using a silicon nitride mask patterned by the proposed PS-b-P4VP surface reconstruction lithography method.