Developing wireless nanodevices and nanosystems are of critical importance for sensing, medical science, defense technology, and even personal electronics. It is highly desirable for wireless devices and even required for implanted biomedical devices that they be self-powered without use of a battery. It is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibrational energy (such as acoustic or ultrasonic waves), and hydraulic energy (such as body fluid now) into electrical energy, which will be used to power nanodevices without it battery. This is it key step towards self-powered nanosystems. We have demonstrated an innovative approach for converting mechanical energy into electrical energy by piezoelectric zinc oxide nanowire (NW) arrays. The operation mechanism of the electric generator relies on the unique coupling of the piezoelectric and semiconducting properties of ZnO as well as the gating effect of the Schottky barrier formed between the metal tip and the NW. Based oil this mechanism, we have recently developed a DC nanogenerator (NG) driven by the ultrasonic wave in a biofluid and a textile-fiber-based NG for harvesting low-frequency mechanical energy. Furthermore, a new field, "nanopiezotronics", has been developed, which uses coupled piezoelectric-semiconducting properties for fabricating novel and unique electronic devices and components. This Feature Article gives it systematic description of the fundamental mechanism of the NG, its rationally innovative design for high output power, and the new electronics that call be built based oil a piezoelectric-driven semiconducting process. A perspective will be given about the future impact of the technologies.