Electrical and structural investigation of AlAs/GaAs/AlAs resonant tunneling structures with pseudomorphic strained Ga1−xInxAs (x=0, 0.05, 0.1, 0.15, and 0.2) emitter spacer layer are presented. As indium composition increased, the peak current density, peak voltage, and peak to valley ratio increased. For a theoretical understanding of these increases, a self-consistent simulation was employed. In the simulation, we treated the 2-dimensional electrons confined in the low energy bandgap GalnAs emitter spacer well as pseudo-3-dimensional electrons, distributed continuously down to the emitter launching energy. In the simulation, we used the bottom energy of the pseudo-3-dimensional electrons to be ⅔δEc below the emitter conduction band edge. Using the above values, an excellent agreement of peak current density and peak voltage between the experiment and the simulation was achieved. Also, for structural identification, standard double crystal x-ray rocking curve technique has been used. From the interference analysis of the x-ray results, we could obtain the indium composition times thickness product.