The infrared absorption and photoresponse characteristics of n-type GaAs/AlxGa1-xAs multiple quantum wells infrared photodetector structure have been studied. With the normal incidence light, a detectivity D*(8.7 mu m)= 1.4 X 10(10) cm Hz(1/2)/W via free-carrier absorption in the wells is achieved at 77 K. This shows a possible fabrication of normal incidence quantum wells infrared photodetector without a grating coupler.