In this paper we propose a novel T-shaped shallow trench isolation technology including an unfilled floating void (VSTI). The structure aims to reduce the dark current in CMOS active pixel sensor technology and is optimized with respect to the size of the depletion region surrounding the STI, also accounting for the leakage current. Simulations outline that a large air void positioned far from the bottom and the top of the T-shaped trench improves performances. (C) 2008 Elsevier Ltd. All rights reserved.