Plasma dry etching, used for the fabrication of low‐dimensional structures, is known to create defects in the material which affect both the optical and the transport properties of the sample. We compare the results obtained from three different methods of characterizing the damage induced by electron cyclotron resonance metalorganic reactive ion etching to the two‐dimensional electron gas (2DEG) in GaAs/AlGaAs heterostructures: photoluminescence, transport measurements, and electron paramagnetic resonance. Etching impairs the quality of luminescence and decreases the single‐particle relaxation time, while the concentration of a surface related paramagnetic defect (probably dangling bonds) is increased. However, detailed experiments show no correlation between the density of defects and transport or luminescence properties, nor between transport and luminescence properties. In particular, hydrogen passivation, which improves the luminescence properties after etching, leads to deteriorated transport properties. ©1995 American Institute of Physics.