A normal incidence quantum well infrared photodetector consisting of asymmetric GaAs/AlGaAs quantum wells has been demonstrated. The detector uses electron intersubband transitions between bound to extended states in the step quantum well. The infrared photocurrent spectrum characterized using a glowbar monochromator source shows a photovoltaic response in the configuration of normal incidence. The peak wavelength is 10.3 μm and a detectivity Dλ*=3.7×108 cm √Hz/W was achieved at T=80 K.