although 
 the various effects of strain on silicon are subject of intensive 
 research since the 1950s the physical background of anomalous piezoresistive 
 effects in si nanowires ( nws ) is still under debate . 
 recent investigations 
 concur in that due to the high surface - to - volume ratio extrinsic surface 
 related effects superimpose the intrinsic piezoresistive properties 
 of nanostructures . to clarify this interplay of piezoresistive effects 
 and stress related surface potential modifications 
 , we explored a 
 particular tensile straining device ( tsd ) with a monolithic embedded 
 vapor  liquid  solid ( vls ) grown si nw . 
 integrating the 
 suspended nw in a gate all around ( gaa ) field effect transistor ( fet ) 
 configuration with a transparent gate stack enables optical and field 
 modulated electrical characterization under high uniaxial tensile 
 strain applied along the 111 si nw growth direction . 
 a model based on stress - induced carrier mobility change and surface 
 charge modulation is proposed to interpret the actual piezoresistive 
 behavior of si nws . by controlling the nature and density of surface 
 states via passivation the  true  piezoresistance of 
 the nws 
 is found to be comparable with that of bulk si . 
 this demonstrates 
 the indispensability of application - specific nw surface conditioning 
 and the modulation capability of si nws properties for sensor applications .