A new semi-analytical solution for a laminar polydisperse spray diffusion flame in the shear layer between fuel and oxidant streams is developed. The liquid phase governing equations are solved using the small Stokes number as a perturbation parameter. The coupled gas-phase equations are treated using the usual inverse of the large Zeldovitch number for the asymptotic analysis. Numerical results demonstrate how the initial droplet size distribution influences the deposition of fuel vapor in the developing shear layer between two unidirectional gas streams flowing over one another with dissimilar velocities in their respective free-streams and thereby impacts on the flame shape, location, fuel vapor and temperature fields. An extinction analysis enables a parametric mapping of conditions for extinguishment of the spray diffusion flames to be drawn.