The effect of planar Si doping on the DX center in AlGaAs is investigated using Capacitance-Voltage and Deep Level Transient Spectroscopy techniques. We observe an increase of approximately six orders of magnitude in the DX center capture cross section in Al.26Ga.74As with planar doped Si spikes of 2×1012cm−2 as compared to conventional homogeneous Si doped Al.26Ga.74As. We also observe a small increase in the DX activation energy which was initiated at a lower planar doping of 4×1011 cm−2 and remained constant for the higher planar doping case. We believe the DX center concentration is not changed by the planar doping levels studied here. A model is proposed to explain the increase in capture cross section based on a biaxial stress state in the planar doped AlGaAs region.