Piezoresistance (PZR) in nano-silicon has long promised to provide a means to sensitively transduce motion in nano-electromechanical systems. Giant or anomalous effects loosely ascribed tomechanically sensitive electronic defects have been reported in lightly doped nano-objects. On the basis of two recent works [1, 2] a quantitative description of the piezoresponse of trap-mediated, space-charge-limited transport will be given. Using silicon nano-membranes containing both native and engineered defects, it will be shown that under steady-state conditions the magnitude of the piezoresistance is always comparable to that of charge-neutral, bulk silicon although a sign change can be induced under bipolar conditions due to stress-induced shifts in the trap activation energies. Under non-steady-state conditions, this same shift in trap activation energies can yield a giant piezoresponse at measurement frequencies close to the characteristic trapping rates. In terms of possible nano-sensing applications, the difficulties likely to be encountered when trying to exploit this giant piezo-impedance will be discussed.