Disclosed is a method of forming an integrated circuit (IC) structure with multiple non-planar transistors having different effective channel widths. In the method, sacrificial gates are removed from partially completed transistors, creating gate openings that expose sections of semiconductor fins between source/drain regions. Prior to forming replacement metal gates in the gate openings, additional process steps are performed so that, in the resulting IC structure, some transistors have different channel region heights and, thereby different effective channel widths, than others. These steps can include forming isolation regions in the bottoms of some gate openings. Additionally or alternatively, these steps can include filling some gate openings with a sacrificial material, recessing the sacrificial material to expose fin tops within those gate openings, either recessing the fin tops or forming isolation regions in the fin tops, and removing the sacrificial material. Also disclosed is an IC structure formed according to the method.