A method and structure for a semiconductor device that includes one or more fin-type field effect transistors (FINFETs) and single-diffusion break (SDB) type isolation regions, which are within a semiconductor fin and define the active device region(s) for the FINFET(s). Asymmetric trenches are formed in a substrate through asymmetric cuts in sacrificial fins formed on the substrate. The asymmetric cuts have relatively larger gaps between fin portions that are closest to the substrate, and deeper portions of the asymmetric trenches are relatively wider than shallower portions. Channel regions are formed in the substrate below two adjacent fins. Source/drain regions of complementary transistors are formed in the substrate on opposite sides of the channel regions. The asymmetric trenches are filled with an insulator to form a single-diffusion break between two source/drain regions of different ones of the complementary transistors. Also disclosed is a semiconductor structure formed according to the method.