Vertically aligned Si nanoconstrictions have potential for applications of electronic, photonic and phononic nanodevices. Herein, we report a featured method by utilizing the non-uniaxial tangential tension stress (σT) at the Si surface of a vertical hyperbolic Si/SiO2 core–shell nanostructure during thermal oxidation to achieve well defined Si nanoconstrictions. A thermal oxidation model was proposed to describe the correlations between σT and the structural parameters of the hyperbolic nanostructure, i.e. oxide thickness (tox), sidewall curvature radius (R0) and neck diameter (2rA0). Numerical simulations indicated that the Si surface at the position with the narrowest diameter (neck position) has the highest σT (~GPa) and presents a gradient distribution at both ends. By means of stress regulation, an array of well defined Si nanoconstrictions about 10 nm in diameter and about 34 nm in length was obtained. The experimental findings demonstrated that the high σT would induce a nanofracture and thus a local oxidation to form a nanoconstriction, self-aligned at the neck position. The finding notably extends the capability of stress-assisted 'nanofabrication' of Si via thermal oxidation.