We investigated the screening effect on the Fock exchange and argued that the effect strongly improves the bandgap description. In this Letter, we propose a screened Fock potential, and the screened Fock exchange method yields diamond's bandgap values which are very close to the experimentally obtained values. We also compared the band structures obtained by using the Hartee-Fock (HF) approximation and the density functional theory (DFT). (C) 2008 Elsevier B.V. All rights reserved.