We have designed and fabricated a quantum dot infrared photodetector which utilizes the lateral transport of photoexcited carriers in the A1GaAs/GaAs two-dimensional (2D) channels. A photocurrent signal has been observed in the range of 9.5-11 mum with a peak at 10.5 mum due to the buund-to-continuum intersubband absorption of the normal incidence radiation in the self-assembled InAs quantum dots. The peak detectivity was measured to be 1 x 10(9) om Hz(1/2)/W at 220K. The high detectivity is realized mainly by low dark current, high mobility and a long lifetime of photoexcited carriers in the modulation doped 2D channels.