A wide-bandgap SiC4 semiconductor with low density and high elasticity has been designed and characterized by ab initio molecular dynamics simulations and first-principles calculations.The through-space conjugation among the d orbitals of Si and the π* orbitals of ethynyl moieties can remarkably enhance the photoconductivity.This new-type superlight and superflexible semiconductor is predicted to have unique electronic,optical,and mechanical properties,and it is a quite promising material for the high-performance UV optoelectronic devices suitable for various practical demands in a complex environment.