We present a theoretical investigation of a novel staircase-like quantum well infrared photodetector (QWIP). The proposed structure makes use of quantum wells and barriers with increasing Al content both in the wells and in the barriers forming a staircase-like energy band diagram without applied bias. The detection wavelength is around lambda = 12 mu m at an applied electric field of F = 1.4 x 10(4) V/cm at room temperature. Device operation is based on inter-subband bound-to-bound transition. We have solved the energy band diagram of the structure self-consistently. We have also calculated the absorption coefficient, responsivity, total net quantum efficiency and dark current density at room temperature. The dark current density at the operating field was found to be around 10(-2) A/cm(2). which is lower than the conventional QWIPs in the literature. (c) 2005 Elsevier B.V. All rights reserved.