Field-effect transistor(FET)requires the channel material to be of both moderate bandgap and high mobility.Few-layer black phosphorus has suitable bandgap and higher mobility than two-dimensional(2D)MoS2,but the experimentally achieved maximal mobility(1000 cm2V-1s-1)is still obviously lower than those of classical semiconductors(1400 and 5400 cm2V-1s-1 for Si and InP).Here,for the first time,we report on monolayer antimonide phosphorus(SbP)as a promising 2D channel material with suitable direct bandgap,which can satisfy the on/off ratio,and with mobility as high as 104 cm2V-1s-1 due to the ultralight hole and electron effective masses.This work reveals that 2D SbP could be a promising candidate as eco-friendly high-performance FET channel materials avoiding short-channel effect in the post-silicon era,especially when considering the recent successful experimental realization of arsenide phosphorus(AsP)with similar structure.