1. Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China

Correspondence to: X. H. Chen¹ Correspondence and requests for materials should be addressed to X.H.C. (Email: chenxh@ustc.edu.cn).

Since the discovery of high-transition-temperature (high-T _c) superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A T _c higher than 40 K (about the theoretical maximum predicted from Bardeen–Cooper–Schrieffer theory¹), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk superconductivity is T _c = 39 K in MgB₂ (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La–Nd, Sm and Gd) are now attracting attention following the discovery of superconductivity at 26 K in the iron-based LaO_1-xF_xFeAs (ref. 3). Here we report the discovery of bulk superconductivity in the related compound SmFeAsO_1-xF_x, which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43 K. This provides a new material base for studying the origin of high-temperature superconductivity.