Abstract The effect of the quantum well (QW) width on the light output and efficiency of ultraviolet (UV) light emitting diodes (LEDs) has been investigated. The carrier injection in the devices is simulated and compared with electroluminescence (EL) measurements. The light output power depends clearly on the QW thickness. The highest output power has been found for the LEDs with a QW thickness of 2.2 nm. This effect is attributed to the trade‐off between electron and hole wave function overlap and carrier concentration in the active region which are triggered by the quantum confined Stark effect.