NOVELTY - Structure includes multiple nano-ribbons (450) or at least one nano-ribbon including multiple nano-ribbon parts, where each of the multiple nano-ribbons corresponds to a first end and a second end. The first end and the second end are separated by a first distance of at least 100 mu m. Each of the multiple nano-ribbons corresponds to a cross-sectional area associated with a ribbon thickness of 5-500 nm; and each of the multiple nano-ribbons is separated from at least another nano-ribbon of the multiple nano-ribbons by a second distance of 5-500 nm.    USE - The structure is useful for thermoelectric devices, and in transistor, solar power converter, battery electrodes and/or energy storage, catalysis, and/or LEDs.    ADVANTAGE - The structure: provides high-performance thermoelectric devices in cost effective manner using less toxic semiconductor materials; is a simple, bulk-like structure having both ultra low thermal conductivity and strong mechanical stiffness at far greater thickness ranges than those for thin-film holey silicon structures; is easily scalable; and provides simplified fabrication of the thermoelectric device element and/or a thermoelectric device with greatly enhanced large-volume manufacturability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a porous structure comprising a porous semiconductor substrate (400) including multiple first voids which are connected with each other, where each of the multiple first voids corresponds to a first cross-sectional area associated with a first distance across that is 5-500 nm and each of the multiple first voids is separated from at least another void by the first distance;    (2) making the structure including nano-ribbons, comprising (a) providing a semiconductor substrate including a first surface that includes first and second portions, (b) forming at least one layer on the first portions of the first surface, where the second portions of the first surface are exposed, and (c) etching the semiconductor substrate through the second portions of the first surface to form at least multiple nano-ribbons; and    (3) making the porous structure, comprising providing the nonporous semiconductor substrate, step (b) as above per se, and etching the nonporous semiconductor substrate through the second portions of the surfaces to form a porous semiconductor substrate including multiple first voids connected with each other.    DESCRIPTION OF DRAWING(S) - The figure shows a process for etching the nano-ribbons to form nanoholes in the sidewalls through the nano-ribbons as a part of the method for making the bulk nanostructure.    Substrate (400)    Multiple nano-ribbons (450)