In this study the improvement in thermal stability of optical properties of InAs submonolayer quantum dot (SML QD) heterostructures is observed through incorporation of symmetric AlGaAs barrier layers. Low temperature photoluminescence (PL) spectra shows blue shift with less full width at half maxima, ascribe to the assimilation of AlGaAs barrier layers. The sample with confinement enhancing barrier shows the highest ground to ground transition energy with the lowest dot size distribution. Ex situ annealing of as grown samples, followed by PL analysis, confirms the improvement in thermal stability of optical behavior. For the samples with symmetric AlGaAs layer, annealing at higher temperatures under an inert condition can not change the downward transition energy effectively, whereas normal DWELL structures exhibits significant blue shift for the same.