By means of the particle-swarm optimization method and density functional theory calculations,the lowestenergy structure of SnAs is determined to be a bilayer stacking system and the atoms on top of each other are of the same types.Using the hybrid functional of Heyd-Scuseria-Ezerhof,SnAs is calculated to be a semiconductor with an indirect band gap of 1.71 eV,which decreases to 1.42eV with the increase of the bi-axial tensile stress up to 2％,corresponding to the ideal value of 1.40eV for potential photovoltaic applications.Based on the deformation potential theory,the two-dimensional (2D) SnAs has high electron motilities along x and y directions (1.63 × 103 cm2 V-1 s-1).Our calculated results suggest that SnAs can be viewed as a new type of 2D materials for applications in optoelectronics and nanoelectronic devices.