A model is presented for the performance of quantum well infrared photodetectors (QWIPs) utilizing intersubband electron transitions and tunneling injection electrons. The dark current and the responsivity are derived as functions of the QWIP parameters, including the number of the QWs, in an analytical form. Nonlinear effects in the QWIP operation at high infrared power are considered and the threshold value of power density is estimated. ©1997 American Institute of Physics.