A search is presented for direct top squark pair production in final states with one isolated electron or muon, jets, and missing transverse momentum in proton-proton collisions at √s=7TeV. The measurement is based on 4.7fb-1 of data collected with the ATLAS detector at the LHC. Each top squark is assumed to decay to a top quark and the lightest supersymmetric particle (LSP). The data are found to be consistent with standard model expectations. Top squark masses between 230GeV and 440GeV are excluded with 95% confidence for massless LSPs, and top squark masses around 400GeV are excluded for LSP masses up to 125GeV. © 2012 CERN.