We report a Raman scattering determination of the energy difference EΓ-L between the Γ conduction-band minimum and the L valley minima in n-type Ga1-xInxAsySb1-y lattice matched to GaSb (x=0.15, y=0.13). A frequency downshift in the L+ phonon–plasmon coupled mode is observed between 80 K and room temperature that is attributed to electron transfer from the Γ to the L valleys. We use the L+ frequency shift to evaluate EΓ-L by performing Lindhard–Mermin L+ line-shape fits for different EΓ-L values. The EΓ-L value increases with electron concentration due to band gap renormalization. A value EΓ-L=154 meV is derived for intrinsic material.