We describe the photoconductive characteristics of a narrow trench-type InGaAs quantum wire field effect transistor (QWR-FET) with a negative differential resistance (NDR). The photoconductive intensity peak of the trench-type QWR was observed at a drain voltage (V-DS) region lower than an onset voltage of NDR (V-NDR), and decreased at the VDS larger than the V-NDR. This result indicates that the carriers transfer from the QWR level to other quantum levels at the V-DS region larger than the V-NDR. By numerically solving the two-dimensional single band Schrodinger equation using the finite element method, we confirm that the carrier can transfer from the high mobility QWR layer to the low mobility sidewall quantum wells, which is thought to be a mechanism of the negative differential resistance of the QWR-FETs. (C) 2004 American Vacuum Society.