Strain-induced quenching of optical transitions has been found in capped self-assembled quantum dot structures. Light absorption at the E 1 and E 1 + Δ 1 critical points of InSb islands buried in InP disappears for nominal InSb thicknesses lower than 10 monolayers as a consequence of the strain produced inside the islands by the cap layer. Certainly, this strain increases as the InSb deposition diminishes, changing the band lineup of the system from type-I to type-II and therefore drastically reducing the oscillator strengths of the island-related E 1 and E 1 + Δ 1 transitions.