Two types of on-chip RFIC transformers based on CMOS compatible strain-induced self-rolled-up membrane (S-RuM) nanotechnology, with extremely small footprint, are demonstrated. The rolled-up transformers, with their 3D tubular form factors, dramatically reduce the substrate parasitic effects and push the maximum working frequency into millimeter wave bands with a coupling coefficient, k, as high as 0.92. The 3D stand-up nature also allows the tube transformers to be less susceptible to residue stress in the substrate and thus compatible with flexible platforms for wearable RF applications. The demonstrated samples with a turn ratio, n, of 5.5:1 only occupies 805 μm2 on-chip area (s) which is 12x smaller than that of the best planar transformer with the same turn ratio, and its figure of merit n·k/s, is therefore ∼ 6046/mm2, enhanced by 15x.