Semiconductor micro- and nano-electromechanical systems (MEMS/NEMS) have the potential to bring about a revolution in the application of semiconductor fine-structure devices, such as high-resolution actuators and sensors, high-frequency signal processing components, and medical diagnostic devices. In addition, when device size reaches the nanometer scale and the characteristic frequency becomes sufficiently high to quantize the freedom of mechanical motion, novel quantum mechanical functions can be introduced. Compared with the commonly used materials systems, such as Si/SiO2 and GaAs/AlGaAs-based heterostructures, InAs-based structures have the advantage that the surface Fermi level pinning in the conduction band makes it possible to fabricate much smaller conductive structures than other semiconductors. We have successfully fabricated a novel piezoresistive stress sensor with a surface InAs conductive layer of nanometer-scale thickness based on MBE-grown InAs/AlGaSb heterostructures. The size of this self-sensing device can be reduced to a nanometer scale and it is expected to be a key component in future MEMS/NEMS applications.